Bio ii 7

Biology II - Zoology

InvertebratesMyriapods

... Figure 33.32 Anatomy of a spider.

Spinnerets

Poisongland

Pedipalp

Brain

Chelicera

Stomach

Spermreceptacle

Heart

... Figure :n.:n A millipede.

Intestine

Silk gland

Digestivegland

Ovary

Anus

and manymites are amonga largegroup ofparasitic arthropods. Nearly all ticks arebloodsucking parasites that live on thebodysurfaces ofreptiles or mammals. Par-asitic mites live on or in a wide variety ofvertebrates, invertebrates, and plants.Arachnids have a cephalothorax that

has six pairs ofappendages: the chelicerae;a pair ofappendages calledpedipalps thatfunction in sensing, feeding, or reproduc-tion; and four pairs of walking legs(Figure 33.32). Spiders use their fang-like chelicerae, which are equipped withpoison glands, to attack prey. As the che-licerae pierce the prey, the spider secretesdigestive juices onto the prey's torn tis-sues. The food softens, and the spidersucks up the liquid meal.In most spiders, gas exchange is car-

ried out by book lungs, stacked platelike structures containedin an internal chamber (see Figure 33.32). The extensive sur-face area of these respiratory organs is a structural adaptationthat enhances the exchange ofO2 and CO2 between the he-molymph and air.A unique adaptation of many spiders is the ability to catch

insects by constructing webs of silk, a liquid protein producedby specialized abdominal glands. The silk is spun by organscalled spinnerets into fibers that then solidify. Each spider en-gineers aweb characteristic of its species and builds it perfectlyon the first try. This complex behavior is apparently inherited.Various spiders also use silk in other ways: as droplines forrapid escape, as a cover for eggs, and even as for foodthat males offer females during courtship. Many small spidersalso extrude silk into the air and let themselves be transportedby wind, a behavior known as

MyriapodsMillipedes and centipedes belong to the subphylumMyriapoda,the myriapods. All living myriapods are terrestrial. The myria-pod head has a pair of antennae and three pairs of appendagesmodified as mouthparts, including the jaw-likemandibles.Millipedes (class Diplopoda) have a large number of

legs, though fewer than the thousand their name implies(Figure 33.33). Each trunk segment is formed from twofused segments and bears two pairs of legs. Millipedes eatdecaying leaves and other plant matter. They may have beenamong the earliest animals on land, living on mosses andprimitive vascular plants.Unlike millipedes, centipedes (class Chilopoda) are carni-

vores. Each segment ofa centipede's trunk region has one pairoflegs (Figure 33.34). Centipedes have poison claws on theirforemost trunk segment that paralyze prey and aid in defense. ... Figure 33.34 A centipede.

CHAPTER THIRTY·THREE Invertebrates 687

... Figure 33.32 Anatomy of a spider.

Spinnerets

Poisongland

Pedipalp

Brain

Chelicera

Stomach

Spermreceptacle

Heart

... Figure :n.:n A millipede.

Intestine

Silk gland

Digestivegland

Ovary

Anus

and manymites are amonga largegroup ofparasitic arthropods. Nearly all ticks arebloodsucking parasites that live on thebodysurfaces ofreptiles or mammals. Par-asitic mites live on or in a wide variety ofvertebrates, invertebrates, and plants.Arachnids have a cephalothorax that

has six pairs ofappendages: the chelicerae;a pair ofappendages calledpedipalps thatfunction in sensing, feeding, or reproduc-tion; and four pairs of walking legs(Figure 33.32). Spiders use their fang-like chelicerae, which are equipped withpoison glands, to attack prey. As the che-licerae pierce the prey, the spider secretesdigestive juices onto the prey's torn tis-sues. The food softens, and the spidersucks up the liquid meal.In most spiders, gas exchange is car-

ried out by book lungs, stacked platelike structures containedin an internal chamber (see Figure 33.32). The extensive sur-face area of these respiratory organs is a structural adaptationthat enhances the exchange ofO2 and CO2 between the he-molymph and air.A unique adaptation of many spiders is the ability to catch

insects by constructing webs of silk, a liquid protein producedby specialized abdominal glands. The silk is spun by organscalled spinnerets into fibers that then solidify. Each spider en-gineers aweb characteristic of its species and builds it perfectlyon the first try. This complex behavior is apparently inherited.Various spiders also use silk in other ways: as droplines forrapid escape, as a cover for eggs, and even as for foodthat males offer females during courtship. Many small spidersalso extrude silk into the air and let themselves be transportedby wind, a behavior known as

MyriapodsMillipedes and centipedes belong to the subphylumMyriapoda,the myriapods. All living myriapods are terrestrial. The myria-pod head has a pair of antennae and three pairs of appendagesmodified as mouthparts, including the jaw-likemandibles.Millipedes (class Diplopoda) have a large number of

legs, though fewer than the thousand their name implies(Figure 33.33). Each trunk segment is formed from twofused segments and bears two pairs of legs. Millipedes eatdecaying leaves and other plant matter. They may have beenamong the earliest animals on land, living on mosses andprimitive vascular plants.Unlike millipedes, centipedes (class Chilopoda) are carni-

vores. Each segment ofa centipede's trunk region has one pairoflegs (Figure 33.34). Centipedes have poison claws on theirforemost trunk segment that paralyze prey and aid in defense. ... Figure 33.34 A centipede.

CHAPTER THIRTY·THREE Invertebrates 687

Millipede(Class Diplopoda)

Centipede(Class Chilopoda)

All living myriapods are terrestrial. The myriapod head has a pair of antennae and three pairs of appendages modified

as mouthparts, including the jaw-like mandibles.

2 leg pairs / segment1 leg pair / segment

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

Arthropods

Tuesday, April 13, 2010

Biology II - Zoology

InvertebratesInsects

Insects and their relatives (subphylum Hexapoda) are more species-rich than all other forms of life combined. They live in almost every terrestrial habitat and in fresh water, and flying insects fill the air. Insects are rare, though not absent, in marine habitats, where crustaceans are the dominant arthropods.

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

Arthropods

Tuesday, April 13, 2010

Biology II - Zoology

InvertebratesThe insect body has three regions: head,thorax, and abdomen. The segmentationof the thorax and abdomen are obvious,but the segments that form the head are fused.

Cerebral ganglion. The two nervecords meet in the head, where theganglia of several anterior segmentsare fused into a cerebral ganglion(brain, colored white below). Theantennae, eyes, and other senseorgans are concentrated on the head.

Insect mouthparts are formed fromseveral pairs of modified appendages.The mouthparts include mandibles,which grasshoppers use for chewing.In other insects, mouthparts arespecialized for lapping, piercing,or sucking.

Nerve cords. The insectnervous systemconsists of a pair ofventral nerve cordswith severalsegmental ganglia.

Heart. The insect heartdrives hemolymphthrough an opencirculatory system.

Compound eye

Vagina

Anus

Malpighian tubules.Metabolic wastes areremoved from the

hemolymph byorgans called Malpighiantubules, which are

out-pocketings of thedigestive tract.

Abdomen Thorax Head.. ...............

Tracheal tubes. Gas exchange in insects isaccomplished by a tracheal system of branched.chitin-lined tubes that infiltrate the body andcarry oxygen directly to cells. The trachealsystem opens to the outside of the bodythrough spiracles, pores that can control airflow and water loss by opening or closing .

... Figure 33.35 Anatomy of a grasshopper, an insect.

Insects

Insects and their relatives (subphylum Hexapoda) are morespecies-rich than all other forms of life combined. They live inalmost every terrestrial habitat and in fresh water, and flying in-sects fill the air. Insects are rare, though not absent, in marinehabitats, where crustaceans are the dominant arthropods. Theinternal anatomy of an insect includes several complex organsystems, which are highlighted in Figure 33.35.The oldest insect fossils date from the Devonian period,

which began about 416 million years ago. However, whenflight evolved during the Carboniferous and Permian periods,it spurred an explosion in insect diversity. Afossil record ofdi-verse insect mouthparts indicates that specialized feeding ongymnosperms and other Carboniferous plants also con-tributed to early adaptive radiations of insects. Later, a majorincrease in insect diversity appears to have been stimulated bythe evolutionary expansion of flowering plants during themid-Cretaceous period (about 90 million years ago). Althoughinsect and plant diversity decreased during the Cretaceousmass extinction, both groups rebounded over the next 65 mil-lion years. Studies indicate that rebounds of particular insectgroups often were associated with radiations of the floweringplants on which they fed.

Flight is obviouslyone key to the great success of insects. Ananimal that can fly can escape many predators, find food andmates, and disperse to newhabitats much faster than an animalthat must crawl about on the ground. Many insects have one ortwo pairs ofwings that emerge from the dorsal side of the tho-rax. Because thewings are extensions ofthe cuticle and not trueappendages, insects can fly without sacrificing any walking legs.By contrast, the flying vertebrates-birds and bats-have oneof their two pairs of walking legs modified into wings, makingsome of these species clumsy on the ground.Inse<t wings may have first evolved as extensions of the cu-

ticle that helped the inse<t body absorb heat, only later be-coming organs for flight. Other hypotheses suggest that wingsallowed terrestrial insects to glide from vegetation to theground or that they served as gills in aquatic insects. Still an-other hypothesis is that insect wings functioned for swimmingbefore they functioned for flight.Morphological and molecular data indicate that wings

evolved onlyonce in insects. Dragonflies, which have two sim-ilar pairs of wings, were among the first insects to fly. Severalinsect orders that evolved later than dragonflies have modifiedflight equipment. The wings of bees and wasps, for instance,are hooked together and move as a single pair. Butterfly wings

688 UNIT fiVE The Evolutionary History of Biological Diversity

Insects

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

Arthropods

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

Arthropods Insects

Oldest insect fossils: Devonian (~416 Ma) Evolution of insect flight: Carboniferous and Permia explosion in insect diversity.

Fossil record of insect mouthparts indicates specialized feeding on gymnosperms and other Carboniferous plants contributed to early adaptive radiations

Major increase in insect diversity stimulated by the evolutionary expansion of flowering plants during the mid-Cretaceous (~ 90 Ma).

Jurrassic beetle

Carboniferous dragonfly

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

Arthropods Insect flight

•one key to great success of insects•facilitates escape from many predators•facilitates discovery of food and mates•facilitates dispersal to new habitats

•one or two pairs of wings emerging from the dorsal side of the thorax

•because wings are extensions of the cuticle and not true appendages, insects can fly without sacrificing any walking legs

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

Arthropods InsectsExploring Insect Diversity,

OrderApproximateNumber ofSpecies

Main Characteristics Examples

8lattodea

Coleoptera

4,""

350.000

Cockroaches ha\'c a dorso\'entrally body, with lqsmodified for rapid running. Forewings hen present, are leath·ery, ",ilereas hind wings are fan6J.:e. F w than 40 cockroKh§Ilt'cies moe in houses; the rest exploit habitUs r.lnging from

forest floors to caves and descn.s.

BcrtIcs comprise the most specks-rich Ofdcr of ins«u. Thq-ha\'e ''''-0 pairs of ",;ngs, one of .....hich is thick and stiff, theother membranous. lbty h;l\'e an armomi nosktltton andmouthPMU adapled for biting and ehe",;ng. BertIes undergocomplete metamorphosis.

Germancockroach

DermaptcnII 1.200 Earwigs are generally nocturnal Ka\'mgers. Sotmo species are'o\ingless, while others ha...e Iwo p,airs of"'ings, one of ....hich isthick and koathery, the other membranous. EalVoigs have bitingmouthparts and large posterior pincer" They undergo incom-plete metamorphosis. Earwig

Diptera

Hemiptera

151,000

85,000

Diptl"I'1UIS ha.\T one pair of .....ings;!.he SCCOlld pair has be<:OITK'modined into balancing organs called haltcrtS. Their mouth-pam are adapll'd for sucking, piercing. or lapping. Dipll."ransundergo complete metamorphosis. Flies and mosquitoes areamong the best·known dipterans, which live as scavengers.predators. and parasites.

Hemipterans are so-called "true bugs; including bed bugs, u·sassin bugs, and chinch bugs. ([nsects in other orders are some·times erroneously called bugs.) Hemipterans have t.....opairs ofwings, one pair partly leathery. the other membranous. Theyhave piercing or sucking mouthparts and undergo incompletemetamorphosis.

Horsefly

Leaf-footedbog

Hymenopten

lsoptcra

125,000

2,""

Ants, bees, and wasps are generally highly social insects. Theyhave two pairs ofmembranous wings. a mobile head. andchewing or sucking mouthparts. The females ofmany spe<ieshave a posterior stinging organ. Hymenopterans undergo com-plete metamorphosis.

Termites are Widespread social ins«ts that produce enormouscolonies. It has been estimated that there are 700 kg oftet'mitesfor every per50Il on Earth! Some termites ha,'e t"'·o pairs ofmembranous ....ings, .....hile others are ....ingless. They f«d on.....ood. ....ith the aid ofmicrobial symbionts carried in spe<ial.izcdchambers in their hindgut.690

Cicad<l-killer wasp

Terrmte

690 UNIT fiVE The Evolutionary History of Biological Diversity

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

Arthropods InsectsExploring Insect Diversity,

OrderApproximateNumber ofSpecies

Main Characteristics Examples

8lattodea

Coleoptera

4,""

350.000

Cockroaches ha\'c a dorso\'entrally body, with lqsmodified for rapid running. Forewings hen present, are leath·ery, ",ilereas hind wings are fan6J.:e. F w than 40 cockroKh§Ilt'cies moe in houses; the rest exploit habitUs r.lnging from

forest floors to caves and descn.s.

BcrtIcs comprise the most specks-rich Ofdcr of ins«u. Thq-ha\'e ''''-0 pairs of ",;ngs, one of .....hich is thick and stiff, theother membranous. lbty h;l\'e an armomi nosktltton andmouthPMU adapled for biting and ehe",;ng. BertIes undergocomplete metamorphosis.

Germancockroach

DermaptcnII 1.200 Earwigs are generally nocturnal Ka\'mgers. Sotmo species are'o\ingless, while others ha...e Iwo p,airs of"'ings, one of ....hich isthick and koathery, the other membranous. EalVoigs have bitingmouthparts and large posterior pincer" They undergo incom-plete metamorphosis. Earwig

Diptera

Hemiptera

151,000

85,000

Diptl"I'1UIS ha.\T one pair of .....ings;!.he SCCOlld pair has be<:OITK'modined into balancing organs called haltcrtS. Their mouth-pam are adapll'd for sucking, piercing. or lapping. Dipll."ransundergo complete metamorphosis. Flies and mosquitoes areamong the best·known dipterans, which live as scavengers.predators. and parasites.

Hemipterans are so-called "true bugs; including bed bugs, u·sassin bugs, and chinch bugs. ([nsects in other orders are some·times erroneously called bugs.) Hemipterans have t.....opairs ofwings, one pair partly leathery. the other membranous. Theyhave piercing or sucking mouthparts and undergo incompletemetamorphosis.

Horsefly

Leaf-footedbog

Hymenopten

lsoptcra

125,000

2,""

Ants, bees, and wasps are generally highly social insects. Theyhave two pairs ofmembranous wings. a mobile head. andchewing or sucking mouthparts. The females ofmany spe<ieshave a posterior stinging organ. Hymenopterans undergo com-plete metamorphosis.

Termites are Widespread social ins«ts that produce enormouscolonies. It has been estimated that there are 700 kg oftet'mitesfor every per50Il on Earth! Some termites ha,'e t"'·o pairs ofmembranous ....ings, .....hile others are ....ingless. They f«d on.....ood. ....ith the aid ofmicrobial symbionts carried in spe<ial.izcdchambers in their hindgut.690

Cicad<l-killer wasp

Terrmte

690 UNIT fiVE The Evolutionary History of Biological Diversity

Exploring Insect Diversity,

OrderApproximateNumber ofSpecies

Main Characteristics Examples

8lattodea

Coleoptera

4,""

350.000

Cockroaches ha\'c a dorso\'entrally body, with lqsmodified for rapid running. Forewings hen present, are leath·ery, ",ilereas hind wings are fan6J.:e. F w than 40 cockroKh§Ilt'cies moe in houses; the rest exploit habitUs r.lnging from

forest floors to caves and descn.s.

BcrtIcs comprise the most specks-rich Ofdcr of ins«u. Thq-ha\'e ''''-0 pairs of ",;ngs, one of .....hich is thick and stiff, theother membranous. lbty h;l\'e an armomi nosktltton andmouthPMU adapled for biting and ehe",;ng. BertIes undergocomplete metamorphosis.

Germancockroach

DermaptcnII 1.200 Earwigs are generally nocturnal Ka\'mgers. Sotmo species are'o\ingless, while others ha...e Iwo p,airs of"'ings, one of ....hich isthick and koathery, the other membranous. EalVoigs have bitingmouthparts and large posterior pincer" They undergo incom-plete metamorphosis. Earwig

Diptera

Hemiptera

151,000

85,000

Diptl"I'1UIS ha.\T one pair of .....ings;!.he SCCOlld pair has be<:OITK'modined into balancing organs called haltcrtS. Their mouth-pam are adapll'd for sucking, piercing. or lapping. Dipll."ransundergo complete metamorphosis. Flies and mosquitoes areamong the best·known dipterans, which live as scavengers.predators. and parasites.

Hemipterans are so-called "true bugs; including bed bugs, u·sassin bugs, and chinch bugs. ([nsects in other orders are some·times erroneously called bugs.) Hemipterans have t.....opairs ofwings, one pair partly leathery. the other membranous. Theyhave piercing or sucking mouthparts and undergo incompletemetamorphosis.

Horsefly

Leaf-footedbog

Hymenopten

lsoptcra

125,000

2,""

Ants, bees, and wasps are generally highly social insects. Theyhave two pairs ofmembranous wings. a mobile head. andchewing or sucking mouthparts. The females ofmany spe<ieshave a posterior stinging organ. Hymenopterans undergo com-plete metamorphosis.

Termites are Widespread social ins«ts that produce enormouscolonies. It has been estimated that there are 700 kg oftet'mitesfor every per50Il on Earth! Some termites ha,'e t"'·o pairs ofmembranous ....ings, .....hile others are ....ingless. They f«d on.....ood. ....ith the aid ofmicrobial symbionts carried in spe<ial.izcdchambers in their hindgut.690

Cicad<l-killer wasp

Terrmte

690 UNIT fiVE The Evolutionary History of Biological Diversity

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

Arthropods InsectsExploring Insect Diversity,

OrderApproximateNumber ofSpecies

Main Characteristics Examples

8lattodea

Coleoptera

4,""

350.000

Cockroaches ha\'c a dorso\'entrally body, with lqsmodified for rapid running. Forewings hen present, are leath·ery, ",ilereas hind wings are fan6J.:e. F w than 40 cockroKh§Ilt'cies moe in houses; the rest exploit habitUs r.lnging from

forest floors to caves and descn.s.

BcrtIcs comprise the most specks-rich Ofdcr of ins«u. Thq-ha\'e ''''-0 pairs of ",;ngs, one of .....hich is thick and stiff, theother membranous. lbty h;l\'e an armomi nosktltton andmouthPMU adapled for biting and ehe",;ng. BertIes undergocomplete metamorphosis.

Germancockroach

DermaptcnII 1.200 Earwigs are generally nocturnal Ka\'mgers. Sotmo species are'o\ingless, while others ha...e Iwo p,airs of"'ings, one of ....hich isthick and koathery, the other membranous. EalVoigs have bitingmouthparts and large posterior pincer" They undergo incom-plete metamorphosis. Earwig

Diptera

Hemiptera

151,000

85,000

Diptl"I'1UIS ha.\T one pair of .....ings;!.he SCCOlld pair has be<:OITK'modined into balancing organs called haltcrtS. Their mouth-pam are adapll'd for sucking, piercing. or lapping. Dipll."ransundergo complete metamorphosis. Flies and mosquitoes areamong the best·known dipterans, which live as scavengers.predators. and parasites.

Hemipterans are so-called "true bugs; including bed bugs, u·sassin bugs, and chinch bugs. ([nsects in other orders are some·times erroneously called bugs.) Hemipterans have t.....opairs ofwings, one pair partly leathery. the other membranous. Theyhave piercing or sucking mouthparts and undergo incompletemetamorphosis.

Horsefly

Leaf-footedbog

Hymenopten

lsoptcra

125,000

2,""

Ants, bees, and wasps are generally highly social insects. Theyhave two pairs ofmembranous wings. a mobile head. andchewing or sucking mouthparts. The females ofmany spe<ieshave a posterior stinging organ. Hymenopterans undergo com-plete metamorphosis.

Termites are Widespread social ins«ts that produce enormouscolonies. It has been estimated that there are 700 kg oftet'mitesfor every per50Il on Earth! Some termites ha,'e t"'·o pairs ofmembranous ....ings, .....hile others are ....ingless. They f«d on.....ood. ....ith the aid ofmicrobial symbionts carried in spe<ial.izcdchambers in their hindgut.690

Cicad<l-killer wasp

Terrmte

690 UNIT fiVE The Evolutionary History of Biological Diversity

Exploring Insect Diversity,

OrderApproximateNumber ofSpecies

Main Characteristics Examples

8lattodea

Coleoptera

4,""

350.000

Cockroaches ha\'c a dorso\'entrally body, with lqsmodified for rapid running. Forewings hen present, are leath·ery, ",ilereas hind wings are fan6J.:e. F w than 40 cockroKh§Ilt'cies moe in houses; the rest exploit habitUs r.lnging from

forest floors to caves and descn.s.

BcrtIcs comprise the most specks-rich Ofdcr of ins«u. Thq-ha\'e ''''-0 pairs of ",;ngs, one of .....hich is thick and stiff, theother membranous. lbty h;l\'e an armomi nosktltton andmouthPMU adapled for biting and ehe",;ng. BertIes undergocomplete metamorphosis.

Germancockroach

DermaptcnII 1.200 Earwigs are generally nocturnal Ka\'mgers. Sotmo species are'o\ingless, while others ha...e Iwo p,airs of"'ings, one of ....hich isthick and koathery, the other membranous. EalVoigs have bitingmouthparts and large posterior pincer" They undergo incom-plete metamorphosis. Earwig

Diptera

Hemiptera

151,000

85,000

Diptl"I'1UIS ha.\T one pair of .....ings;!.he SCCOlld pair has be<:OITK'modined into balancing organs called haltcrtS. Their mouth-pam are adapll'd for sucking, piercing. or lapping. Dipll."ransundergo complete metamorphosis. Flies and mosquitoes areamong the best·known dipterans, which live as scavengers.predators. and parasites.

Hemipterans are so-called "true bugs; including bed bugs, u·sassin bugs, and chinch bugs. ([nsects in other orders are some·times erroneously called bugs.) Hemipterans have t.....opairs ofwings, one pair partly leathery. the other membranous. Theyhave piercing or sucking mouthparts and undergo incompletemetamorphosis.

Horsefly

Leaf-footedbog

Hymenopten

lsoptcra

125,000

2,""

Ants, bees, and wasps are generally highly social insects. Theyhave two pairs ofmembranous wings. a mobile head. andchewing or sucking mouthparts. The females ofmany spe<ieshave a posterior stinging organ. Hymenopterans undergo com-plete metamorphosis.

Termites are Widespread social ins«ts that produce enormouscolonies. It has been estimated that there are 700 kg oftet'mitesfor every per50Il on Earth! Some termites ha,'e t"'·o pairs ofmembranous ....ings, .....hile others are ....ingless. They f«d on.....ood. ....ith the aid ofmicrobial symbionts carried in spe<ial.izcdchambers in their hindgut.690

Cicad<l-killer wasp

Terrmte

690 UNIT fiVE The Evolutionary History of Biological Diversity

Order

Lepidoptera

Odonala

ApproximateNumber ofSpecies

120.000

5.000

Main Characteristics

Butterflies and moths arc amOllg the best-known insects.They have two J»irs of ""ings covered ....ith tiny SQlI('$. Tofeed, they uncoil ill long proboscis. Most ft'rd on n«ur, but$Orne species feed on other substan<:es. including animalblood or tears.

Dragonflies and damselflies han' two J»irs of large.nous '>lings. They N'''' an dongakd abdomen. Large. com-pound and cheo.ooing mouthparts. They undcrgoincompktt metamorphosis and arc active predators.

Examples

SwallowtaIlbutterfly

Dragoofty

Phasmalodea

13.000 Grasshoppers. crickcu. and their rdatin'$ alt' mostly herbr.'O-rous. They have Large hind Iq;s adapted for jumping. '....0 pairsof ....ings (one leathery, one membnnous), and biting orcbew-ing mouthparts. Males commonly make courtship sounds byrubbing togelht-r body palU. such as ill ridge on their hind legs.Orthopterans undergo incomplete mrtamorphosis.

Stick inserts and leaf insects are exquisite mimics of plants.l"he eggs ofsome sjX'Cies e"en mimic seeds orthe plants on....hich the insects live. Their body iscylindrkal or natlenrodorsoventrally. They lack foreWings but have fanlike hind\dngs. Their mouthparts arc adapted for biting or chewing.

Katydid

Stick insect

Phthiraplcr<i

Siphonaplel'll

Trichapten

2.400

2.400

450

7.100

Commonly called sucking lice, these insects spend their entirelife as an ectoparasite feeding on the hair or feathers of a singlehost. Their legs, equipped with clawlike tarsi, are adapted forclinging to their hosts. They lack wings and have reduced eyes.Sucking lice undergo incomplete metamorphosis.

fleas are bloodsucking ectoparasites on birds and mammals.Their body is Wingless and laterally compressed. Their legs aremodified for clinging to their hosts and for long-distance jump-ing. They undergo complete metamorphosis.

Silverfish arc small, Wingless insects with a nauenM body andreduced eycs. They live inleaflittl'l" or under Inri:. Theyanalso infest buildings, whl'l"e they can become pests.

The larvaeofcaddistlies lin' in streams, ,,'here they makehouse'S from sand gr;AiRS•..-ood fragments. or ot.hef materialheld tosether by silk. Adults haw f',Hl pairs of hairy wings andchOling or lapping mouthpalU. They undtrgo complete meta-morphosis.

Humanbodylouse

,

Flea

Silverfish

Caddisfty

lHIUl·TllIIU Invertebrates 691

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

Arthropods InsectsExploring Insect Diversity,

OrderApproximateNumber ofSpecies

Main Characteristics Examples

8lattodea

Coleoptera

4,""

350.000

Cockroaches ha\'c a dorso\'entrally body, with lqsmodified for rapid running. Forewings hen present, are leath·ery, ",ilereas hind wings are fan6J.:e. F w than 40 cockroKh§Ilt'cies moe in houses; the rest exploit habitUs r.lnging from

forest floors to caves and descn.s.

BcrtIcs comprise the most specks-rich Ofdcr of ins«u. Thq-ha\'e ''''-0 pairs of ",;ngs, one of .....hich is thick and stiff, theother membranous. lbty h;l\'e an armomi nosktltton andmouthPMU adapled for biting and ehe",;ng. BertIes undergocomplete metamorphosis.

Germancockroach

DermaptcnII 1.200 Earwigs are generally nocturnal Ka\'mgers. Sotmo species are'o\ingless, while others ha...e Iwo p,airs of"'ings, one of ....hich isthick and koathery, the other membranous. EalVoigs have bitingmouthparts and large posterior pincer" They undergo incom-plete metamorphosis. Earwig

Diptera

Hemiptera

151,000

85,000

Diptl"I'1UIS ha.\T one pair of .....ings;!.he SCCOlld pair has be<:OITK'modined into balancing organs called haltcrtS. Their mouth-pam are adapll'd for sucking, piercing. or lapping. Dipll."ransundergo complete metamorphosis. Flies and mosquitoes areamong the best·known dipterans, which live as scavengers.predators. and parasites.

Hemipterans are so-called "true bugs; including bed bugs, u·sassin bugs, and chinch bugs. ([nsects in other orders are some·times erroneously called bugs.) Hemipterans have t.....opairs ofwings, one pair partly leathery. the other membranous. Theyhave piercing or sucking mouthparts and undergo incompletemetamorphosis.

Horsefly

Leaf-footedbog

Hymenopten

lsoptcra

125,000

2,""

Ants, bees, and wasps are generally highly social insects. Theyhave two pairs ofmembranous wings. a mobile head. andchewing or sucking mouthparts. The females ofmany spe<ieshave a posterior stinging organ. Hymenopterans undergo com-plete metamorphosis.

Termites are Widespread social ins«ts that produce enormouscolonies. It has been estimated that there are 700 kg oftet'mitesfor every per50Il on Earth! Some termites ha,'e t"'·o pairs ofmembranous ....ings, .....hile others are ....ingless. They f«d on.....ood. ....ith the aid ofmicrobial symbionts carried in spe<ial.izcdchambers in their hindgut.690

Cicad<l-killer wasp

Terrmte

690 UNIT fiVE The Evolutionary History of Biological Diversity

Order

Lepidoptera

Odonala

ApproximateNumber ofSpecies

120.000

5.000

Main Characteristics

Butterflies and moths arc amOllg the best-known insects.They have two J»irs of ""ings covered ....ith tiny SQlI('$. Tofeed, they uncoil ill long proboscis. Most ft'rd on n«ur, but$Orne species feed on other substan<:es. including animalblood or tears.

Dragonflies and damselflies han' two J»irs of large.nous '>lings. They N'''' an dongakd abdomen. Large. com-pound and cheo.ooing mouthparts. They undcrgoincompktt metamorphosis and arc active predators.

Examples

SwallowtaIlbutterfly

Dragoofty

Phasmalodea

13.000 Grasshoppers. crickcu. and their rdatin'$ alt' mostly herbr.'O-rous. They have Large hind Iq;s adapted for jumping. '....0 pairsof ....ings (one leathery, one membnnous), and biting orcbew-ing mouthparts. Males commonly make courtship sounds byrubbing togelht-r body palU. such as ill ridge on their hind legs.Orthopterans undergo incomplete mrtamorphosis.

Stick inserts and leaf insects are exquisite mimics of plants.l"he eggs ofsome sjX'Cies e"en mimic seeds orthe plants on....hich the insects live. Their body iscylindrkal or natlenrodorsoventrally. They lack foreWings but have fanlike hind\dngs. Their mouthparts arc adapted for biting or chewing.

Katydid

Stick insect

Phthiraplcr<i

Siphonaplel'll

Trichapten

2.400

2.400

450

7.100

Commonly called sucking lice, these insects spend their entirelife as an ectoparasite feeding on the hair or feathers of a singlehost. Their legs, equipped with clawlike tarsi, are adapted forclinging to their hosts. They lack wings and have reduced eyes.Sucking lice undergo incomplete metamorphosis.

fleas are bloodsucking ectoparasites on birds and mammals.Their body is Wingless and laterally compressed. Their legs aremodified for clinging to their hosts and for long-distance jump-ing. They undergo complete metamorphosis.

Silverfish arc small, Wingless insects with a nauenM body andreduced eycs. They live inleaflittl'l" or under Inri:. Theyanalso infest buildings, whl'l"e they can become pests.

The larvaeofcaddistlies lin' in streams, ,,'here they makehouse'S from sand gr;AiRS•..-ood fragments. or ot.hef materialheld tosether by silk. Adults haw f',Hl pairs of hairy wings andchOling or lapping mouthpalU. They undtrgo complete meta-morphosis.

Humanbodylouse

,

Flea

Silverfish

Caddisfty

lHIUl·TllIIU Invertebrates 691

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

Arthropods InsectsExploring Insect Diversity,

OrderApproximateNumber ofSpecies

Main Characteristics Examples

8lattodea

Coleoptera

4,""

350.000

Cockroaches ha\'c a dorso\'entrally body, with lqsmodified for rapid running. Forewings hen present, are leath·ery, ",ilereas hind wings are fan6J.:e. F w than 40 cockroKh§Ilt'cies moe in houses; the rest exploit habitUs r.lnging from

forest floors to caves and descn.s.

BcrtIcs comprise the most specks-rich Ofdcr of ins«u. Thq-ha\'e ''''-0 pairs of ",;ngs, one of .....hich is thick and stiff, theother membranous. lbty h;l\'e an armomi nosktltton andmouthPMU adapled for biting and ehe",;ng. BertIes undergocomplete metamorphosis.

Germancockroach

DermaptcnII 1.200 Earwigs are generally nocturnal Ka\'mgers. Sotmo species are'o\ingless, while others ha...e Iwo p,airs of"'ings, one of ....hich isthick and koathery, the other membranous. EalVoigs have bitingmouthparts and large posterior pincer" They undergo incom-plete metamorphosis. Earwig

Diptera

Hemiptera

151,000

85,000

Diptl"I'1UIS ha.\T one pair of .....ings;!.he SCCOlld pair has be<:OITK'modined into balancing organs called haltcrtS. Their mouth-pam are adapll'd for sucking, piercing. or lapping. Dipll."ransundergo complete metamorphosis. Flies and mosquitoes areamong the best·known dipterans, which live as scavengers.predators. and parasites.

Hemipterans are so-called "true bugs; including bed bugs, u·sassin bugs, and chinch bugs. ([nsects in other orders are some·times erroneously called bugs.) Hemipterans have t.....opairs ofwings, one pair partly leathery. the other membranous. Theyhave piercing or sucking mouthparts and undergo incompletemetamorphosis.

Horsefly

Leaf-footedbog

Hymenopten

lsoptcra

125,000

2,""

Ants, bees, and wasps are generally highly social insects. Theyhave two pairs ofmembranous wings. a mobile head. andchewing or sucking mouthparts. The females ofmany spe<ieshave a posterior stinging organ. Hymenopterans undergo com-plete metamorphosis.

Termites are Widespread social ins«ts that produce enormouscolonies. It has been estimated that there are 700 kg oftet'mitesfor every per50Il on Earth! Some termites ha,'e t"'·o pairs ofmembranous ....ings, .....hile others are ....ingless. They f«d on.....ood. ....ith the aid ofmicrobial symbionts carried in spe<ial.izcdchambers in their hindgut.690

Cicad<l-killer wasp

Terrmte

690 UNIT fiVE The Evolutionary History of Biological Diversity

Order

Lepidoptera

Odonala

ApproximateNumber ofSpecies

120.000

5.000

Main Characteristics

Butterflies and moths arc amOllg the best-known insects.They have two J»irs of ""ings covered ....ith tiny SQlI('$. Tofeed, they uncoil ill long proboscis. Most ft'rd on n«ur, but$Orne species feed on other substan<:es. including animalblood or tears.

Dragonflies and damselflies han' two J»irs of large.nous '>lings. They N'''' an dongakd abdomen. Large. com-pound and cheo.ooing mouthparts. They undcrgoincompktt metamorphosis and arc active predators.

Examples

SwallowtaIlbutterfly

Dragoofty

Phasmalodea

13.000 Grasshoppers. crickcu. and their rdatin'$ alt' mostly herbr.'O-rous. They have Large hind Iq;s adapted for jumping. '....0 pairsof ....ings (one leathery, one membnnous), and biting orcbew-ing mouthparts. Males commonly make courtship sounds byrubbing togelht-r body palU. such as ill ridge on their hind legs.Orthopterans undergo incomplete mrtamorphosis.

Stick inserts and leaf insects are exquisite mimics of plants.l"he eggs ofsome sjX'Cies e"en mimic seeds orthe plants on....hich the insects live. Their body iscylindrkal or natlenrodorsoventrally. They lack foreWings but have fanlike hind\dngs. Their mouthparts arc adapted for biting or chewing.

Katydid

Stick insect

Phthiraplcr<i

Siphonaplel'll

Trichapten

2.400

2.400

450

7.100

Commonly called sucking lice, these insects spend their entirelife as an ectoparasite feeding on the hair or feathers of a singlehost. Their legs, equipped with clawlike tarsi, are adapted forclinging to their hosts. They lack wings and have reduced eyes.Sucking lice undergo incomplete metamorphosis.

fleas are bloodsucking ectoparasites on birds and mammals.Their body is Wingless and laterally compressed. Their legs aremodified for clinging to their hosts and for long-distance jump-ing. They undergo complete metamorphosis.

Silverfish arc small, Wingless insects with a nauenM body andreduced eycs. They live inleaflittl'l" or under Inri:. Theyanalso infest buildings, whl'l"e they can become pests.

The larvaeofcaddistlies lin' in streams, ,,'here they makehouse'S from sand gr;AiRS•..-ood fragments. or ot.hef materialheld tosether by silk. Adults haw f',Hl pairs of hairy wings andchOling or lapping mouthpalU. They undtrgo complete meta-morphosis.

Humanbodylouse

,

Flea

Silverfish

Caddisfty

lHIUl·TllIIU Invertebrates 691

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

.. Figure 33.25 Afree-living nematode (colorized SEM),

Nematodes

Muscle tissueEncysted juveniles

... Figure 33.26 Juveniles of the parasitic nematodeTrichinella spiralis encysted in human muscle tissue (LM).

Multitudes ofnematodes live in moist soil and in decompos-ing organic matter on the bottoms of lakes and oceans. While25,000 species are known, perhaps 20 times that number actu-ally exist. It has been said that if nothing but nematodes re-mained on Earth, they would still preserve the outline of theplanet and many onts features. These free-living worms play animportant role in decomposition and nutrient cycling, but littleis known about most species. One species of soil nematode,Caellorhabditis elegalls, however, is very well studied and hasbecome a model research organism in biology (see Chapter 21).Ongoing studies on C. elegans are revealing some of the mech-anisms involved in aging in humans, among other findings.Phylum Nematoda includes many significant agricultural

pests that attack the roots ofplants. Other speciesofnematodesparasitize animals. Humans are hosts to at least 50 nematodespecies, including various pinworms and hookworms. One no-torious nematode is Trichinella spiralis, the worm that causestrichinosis (Figure 33.26). Humans acquire this nematode byeating raw or undercooked pork or other meat (including wildgame such as bear or walrus) that has juvenileworms encystedin the muscle tissue. \'(!ithin the human intestines, the juvenilesdevelop into sexually mature adults. Females burrow into theintestinal muscles and produce more juveniles, which borethrough the body or travel in lymphatic vessels to other organs,including skeletal muscles, where they encyst.Parasitic nematodes have an extraordinary molecular

toolkit that enables them to redirect some of the cellular func-tions of their hosts and thus evade their immune systems.Plant-parasitic nematodes inject molecules that induce thedevelopment of root cells, which then supply nutrients to theparasites. Trichinella controls the expression of specificmuscle-cell genes that code for proteins that make the cell elas-tic enough to house the nematode. Additionally, the infectedmuscle cell releases signals that attract blood vessels, which

Although defined primarily bymolecular evidence, the dadeEcdysozoa includes animalsthat shed a tough external coat(cuticle) as they grow; in fact,

the group derives its name from this process, which is calledmolting, or ecdysis. Ecdysozoa consists of about eight animalphyla and contains mOTe known species than all other protist,fungus, plant, and animal groups combined. Here we'll focuson the two largest e<dysozoan phyla, the nematodes andarthropods, which are among the most successful and abun-dant of all animal groups.

the mostspecies-rich animal group

Some of the most ubiquitous animals, nematodes (phylumNematoda), or roundworms, are found in most aquatic habitats,in the soil, in the moist tissues of plants, and in the body fluidsand tissues of animals. In contrast to annelids, nematodes donot have segmented bodies. The cylindrical bodies of nema-todes range from less than 1mm to more than ameter in length,often tapering to a fine tip at the posterior end and to a moreblunt tip at the anterior end (Figure 33.25). Anematode's bodyis covered by a tough cuticle; as the worm grows, it periodicallysheds its old cuticle and secretes a new, larger one. Nematodeshave an alimentary canal, though they lack a circulatory system.Nutrients are transported throughout the body via fluid in thepseudocoelom. The body wall muscles are all longitudinal, andtheir contraction produces a thrashing motion.Nematodes usually reproduce sexually, by internal fertiliza-

tion. In most species, the sexes are separate and females arelarger than males. A female may deposit 100,000 or more fer-tilized eggs (zygotes) per day. The zygotes of most species areresistant cells that can survive harsh conditions.

r;;==; Calcarea and SiliceaCmdanaLopholnxhowaEcdysozoaDeuterostorma

CHAPTER THIRTY·THREE Invertebrates 683

(a) Ghost crabs live on sandy ocean beaches worldwide. Pnmarilynocturnal. they take shelter In burrows dunng the day_

(el The JOinted appendagesprOjectlng from the shellsof these barnacles captureorganISms and organicpartlCles suspended inthe water.

CONCEPT CHECK 33.4I. How do nematode and annelid body plans differ?2. In contrast to our jaws. which move up and down, themouthparts ofarthropods move side to side. Explainthis feature ofarthropods in terms of the origin oftheir mouthparts.

3. Describe two adaptations that have enabled insects tothrive on land.

4. -lim i1iM Traditionally. annelids and arthropodswere thought to be closely related because bothgroups show body segmentation. Yet molecular dataindicate that annelids belong to one clade(Lophotrochozoa) and arthropods to another(Ecdysozoa). Could traditional and molecular hy-potheses be tested by studying the expression ofHoxgenes that control body segmentation? Explain.For suggested answers. see Appendix A. -..J

(b) Planktonic crustaceans knownas I:::rin are consumed In vastquantities by some whales.

• Figure 33.38 Crustaceans.

Crustaceans\Vhjle arachnids and insects thrive on land, crustaceans, for themost part. have remained in marine and freshwater environ-ments.Crustlre.ms Crustlce,) typicallyM"highlyspecialized appendages. Lobsters and crayfIShes, for instance.have a toolkit of 19 pairs ofappendages 33.29). Theanteriormost appendages are antennae; crustaceans are theonly arthropods with two pairs. Three or more pairs of ap-pendages are modified as mouthparts. including the hardmandibles. Walking legs are present on the thorax, and, unlikeinsects, crustaceans also have appendages on their abdomen.Alost appendage can be regenerated at next molt.Small crustaceans exchange gases across thin areas of the

cuticle; larger species have gills. Nitrogenous ....'astes also dif-fuse through thin areas of the cuticle. but a pair ofglands reg-ulates the salt balance of the hemolymph.Sexes are separate in most crustaceans. In the case of lob-

sters and crayfish. the male uses a specialized pair ofabdomi-nal appendages to transfer sperm to the reproductive pore ofthe female during copulation. Most aquatic crustaceans gothrough one or more swimming larval stages.One ofthe largest groups ofcrustaceans (numbering about

IO,lXX') species) is the isopods, which include terrestrial. fresh·water, and marine species. Some isopod species are abundantin habitats at the bottom of the deep ocean. Among the ter·restrial isopods are the pill bugs. or wood lice. common on theundersides ofmoist logs and leaves.Lobsters. crayfishes. crabs. and shrimpsare all large

crust:aceanscalleddecapods (Figure 33.38a). Thecuticleofde-capods is hardened by calcium carbonate; the portion that cov-ers the dorsal side ofthe cephalothorax forms a shield called thecarapace. Most decapod species are marine. Crayfishes, how-ever, live in fresh water, and some tropical crabs live on land.Many small crustaceans are important members of marine

and freshwater plankton communities. Planktonic crustaceansinclude many species ofcopcpods, which are among the mostnumerous of all animals, as well as the shrimplike krill, whichgrow to about 5 cm long (Figure 33.38b). A major food sourcefor baleen whales (indudingblue whales. humpbacks, and rightwhales), krill are now being harvested in great numbers by hu-mans for food and agricultural fertilizer. The larvae of manylarger-bodied crustaceans are also planktonic.Barnacles are a group ofmostly sessile austaceans ....t\ose cu-

tide is hardened into a sheI.I containing ca.kium carbonate(FtgUre 33.38c). Most bamades anchor tIlernseh'eS to rocks, boathulls, pilings, ,00 othe<sub"""ll"d...raa.. Thek nalur.l!_.is as strong as synthetic glues. To feed. these barnacles extend ap-pendages from their shell to strain food from the wat:el: Bamadeswere not rerogniz.ed as crustaceans until the when naturoJ·ists discovered that bamacIe larvae resemble the larvae of othercrustaceans. The remarkable mix of unique traits and crustareanhomologies fourKI. in barnacles was a major inspiration to OiarlesDarwin as he developed his theory ofevolution.

692 UNIT fiVE The Evolutionary History of Biological Diversity

Crustaceans

(a) Ghost crabs live on sandy ocean beaches worldwide. Pnmarilynocturnal. they take shelter In burrows dunng the day_

(el The JOinted appendagesprOjectlng from the shellsof these barnacles captureorganISms and organicpartlCles suspended inthe water.

CONCEPT CHECK 33.4I. How do nematode and annelid body plans differ?2. In contrast to our jaws. which move up and down, themouthparts ofarthropods move side to side. Explainthis feature ofarthropods in terms of the origin oftheir mouthparts.

3. Describe two adaptations that have enabled insects tothrive on land.

4. -lim i1iM Traditionally. annelids and arthropodswere thought to be closely related because bothgroups show body segmentation. Yet molecular dataindicate that annelids belong to one clade(Lophotrochozoa) and arthropods to another(Ecdysozoa). Could traditional and molecular hy-potheses be tested by studying the expression ofHoxgenes that control body segmentation? Explain.For suggested answers. see Appendix A. -..J

(b) Planktonic crustaceans knownas I:::rin are consumed In vastquantities by some whales.

• Figure 33.38 Crustaceans.

Crustaceans\Vhjle arachnids and insects thrive on land, crustaceans, for themost part. have remained in marine and freshwater environ-ments.Crustlre.ms Crustlce,) typicallyM"highlyspecialized appendages. Lobsters and crayfIShes, for instance.have a toolkit of 19 pairs ofappendages 33.29). Theanteriormost appendages are antennae; crustaceans are theonly arthropods with two pairs. Three or more pairs of ap-pendages are modified as mouthparts. including the hardmandibles. Walking legs are present on the thorax, and, unlikeinsects, crustaceans also have appendages on their abdomen.Alost appendage can be regenerated at next molt.Small crustaceans exchange gases across thin areas of the

cuticle; larger species have gills. Nitrogenous ....'astes also dif-fuse through thin areas of the cuticle. but a pair ofglands reg-ulates the salt balance of the hemolymph.Sexes are separate in most crustaceans. In the case of lob-

sters and crayfish. the male uses a specialized pair ofabdomi-nal appendages to transfer sperm to the reproductive pore ofthe female during copulation. Most aquatic crustaceans gothrough one or more swimming larval stages.One ofthe largest groups ofcrustaceans (numbering about

IO,lXX') species) is the isopods, which include terrestrial. fresh·water, and marine species. Some isopod species are abundantin habitats at the bottom of the deep ocean. Among the ter·restrial isopods are the pill bugs. or wood lice. common on theundersides ofmoist logs and leaves.Lobsters. crayfishes. crabs. and shrimpsare all large

crust:aceanscalleddecapods (Figure 33.38a). Thecuticleofde-capods is hardened by calcium carbonate; the portion that cov-ers the dorsal side ofthe cephalothorax forms a shield called thecarapace. Most decapod species are marine. Crayfishes, how-ever, live in fresh water, and some tropical crabs live on land.Many small crustaceans are important members of marine

and freshwater plankton communities. Planktonic crustaceansinclude many species ofcopcpods, which are among the mostnumerous of all animals, as well as the shrimplike krill, whichgrow to about 5 cm long (Figure 33.38b). A major food sourcefor baleen whales (indudingblue whales. humpbacks, and rightwhales), krill are now being harvested in great numbers by hu-mans for food and agricultural fertilizer. The larvae of manylarger-bodied crustaceans are also planktonic.Barnacles are a group ofmostly sessile austaceans ....t\ose cu-

tide is hardened into a sheI.I containing ca.kium carbonate(FtgUre 33.38c). Most bamades anchor tIlernseh'eS to rocks, boathulls, pilings, ,00 othe<sub"""ll"d...raa.. Thek nalur.l!_.is as strong as synthetic glues. To feed. these barnacles extend ap-pendages from their shell to strain food from the wat:el: Bamadeswere not rerogniz.ed as crustaceans until the when naturoJ·ists discovered that bamacIe larvae resemble the larvae of othercrustaceans. The remarkable mix of unique traits and crustareanhomologies fourKI. in barnacles was a major inspiration to OiarlesDarwin as he developed his theory ofevolution.

692 UNIT fiVE The Evolutionary History of Biological Diversity

•live marine and freshwater environments; typically have highly specialized appendages•anteriormost appendages are antennae; crustaceans are the only arthropods with two pairs

Three or more pairs of appendages are modified as mouthparts, including the hard mandibles Walking legs are present on the thorax, and, unlike insects, crustaceans also have appendages on their abdomen. A lost appendage can be regenerated at next molt.

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

Echinoderms

Deuterostomia is defined primarily by DNA similarities-notdevelopmental similarities.

Sea stars and most other echinoderms (from the Greek echin,spiny, and derma, skin) are slow-moving or sessile marine an-imals. A thin epidermis covers an endoskeleton of hard cal-careous plates. Most echinoderms are prickly from skeletalbumps and spines. Unique to echinoderms is the watervascular system, a network ofhydraulic canals branching intoextensions called tube feet that function in locomotion, feed-ing, and gas exchange (Figure 33.39). Sexual reproduction ofechinoderms usually involves separate male and female indi-viduals that release their gametes into the water.The internal and external parts of most adult echinoderms

radiate from the center, often as five spokes. However, echin-oderm larvae have bilateral symmetry. Furthermore, the sym-metry of adult echinoderms is not truly radial. For example,the opening (madreporite) ofa sea star's water vascular systemis not central but shifted to one side.

are

Sea stars, sea urchins, and othere<hinoderms (phylumdermata) may seem to have lit-tle in common with phylumChordata, which includes the

vertebrates-animals that have a backbone. In fact, however,echinoderms and chordates share features characteristic of adeuterostome mode of development, such as radial cleavageand formation of the mouth at the end of the embryo oppositethe blastopore (see Figure 32.9). Molecular systematics has re-inforced Deuterostomia as a clade of bilaterian animals. Butmolecular evidence also indicates that some animal phyla withmembers that have deuterostome developmental features, in-cluding ectoprocts and brachiopods, are not in the deutero-stome dade (see Chapter 32). Hence, despite its name, the clade

chordatesdeuterostomes

! CmdanaLopholrochozoaEcdysozoaDeuterostomia

Madreporite. Watercan flow in or outof the water vascularsystem into thesurrounding waterthrough themadreporite.

The surface of a sea star iscovered by spines that helpdefend against predators, aswell as by small gills thatprovide gas exchange.

Each tube foot consists of a bulb-like ampulla and a podium (footportion). When the ampulla squeezes. water is forced into the podium,which expands and contacts the substrate. Adhesive chemicals are thensecreted from the base of the podium, attaching it to the substrate. Todetach the tube foot, de-adhesive chemicals are secreted and musclesin the podium contract, forcing water back into the ampulla andshortening the podium. As it moves, a sea star leaves an observableNfootprint H of adhesive material on the substrate.

Radial canal. The water vascularsystem consists of a ring canal in thecentral disk and five radial canals,each running in a groove down theentire length of an arm. Branchingfrom each radial canal are hundredsof hollow, muscular tube feet filledwith fluid.

Ashort digestive tract runs from themouth on the bottom of the centraldisk to the anus on top of the disk.

/

Central disk. The central diskrhas a nerve ring and nerve

cords radiating from the ringinto the arms.

Digestive glands secretedigestive juices and aid in the

absorption and storageof nutrients.

... Figure 33.39 Anatomy of a sea star, an echinoderm.

CHAPTER THIRTY·THREE Invertebrates 693

Echinoderms

Echinoderms are deuterostomes.

Molecular systematics has reinforced Deuterostomia as a clade of bilaterian animals. But molecular evidence also indicates that some animal phyla with members that have deuterostome developmental features, including ectoprocts and brachiopods, are not in the deuterostome clade. Hence, despite its name, the clade Deuterostomia is defined primarily by DNA similarities, not developmental similarities.

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

(a) Asea star (class Asteroidea)

«) Asea urchin (class E(hinoidea)

(e) Asea cucumber (class Holothuroidea).. Figure 33.40 Echinoderms.

(b) Abrittle star (class Ophiuroidea)

(d) Afeather star (class Crinoidea)

(f) A sea daisy (class Con(entricycloidea)

1. Describe how sea star tube feet attach to substrates.2. Are characteristics shared by a sea star and a sea daisyhomologous or analogous? Explain.

3.•i,il:O'I,. The insectDrosophila me/anogaslerandthe nematode Caenurhabditis e/egans are prominentmodel organisms. Are these species the most appro-priate invertebrates for making inferences about hu-mans and other vertebrates in Deuterostomia? Explain.For suggested answers. see AppendiK A.

ChordalesPhylum Chordata consists ofm'o subphyla of invertebrates aswell as the hagfishes and the vertebrates. Chordates are bilat-erally symmetrical coelomates with segmented bodies. Thedose relationship between echinoderms and chordates doesnot mean that one phylum evolved from the other. In fact,echinoderms and chordates have evolved independently ofone another for at least 500 million years. We will trace thephylogeny ofchordates in Chapter 34, focusing on the historyof vertebrates.

CONCEPT CHECK 33.5

(HAPTER THIRTY·THREE Invertebrates 695

Echinodermata

Echinoderms

Deuterostomia is defined primarily by DNA similarities-notdevelopmental similarities.

Sea stars and most other echinoderms (from the Greek echin,spiny, and derma, skin) are slow-moving or sessile marine an-imals. A thin epidermis covers an endoskeleton of hard cal-careous plates. Most echinoderms are prickly from skeletalbumps and spines. Unique to echinoderms is the watervascular system, a network ofhydraulic canals branching intoextensions called tube feet that function in locomotion, feed-ing, and gas exchange (Figure 33.39). Sexual reproduction ofechinoderms usually involves separate male and female indi-viduals that release their gametes into the water.The internal and external parts of most adult echinoderms

radiate from the center, often as five spokes. However, echin-oderm larvae have bilateral symmetry. Furthermore, the sym-metry of adult echinoderms is not truly radial. For example,the opening (madreporite) ofa sea star's water vascular systemis not central but shifted to one side.

are

Sea stars, sea urchins, and othere<hinoderms (phylumdermata) may seem to have lit-tle in common with phylumChordata, which includes the

vertebrates-animals that have a backbone. In fact, however,echinoderms and chordates share features characteristic of adeuterostome mode of development, such as radial cleavageand formation of the mouth at the end of the embryo oppositethe blastopore (see Figure 32.9). Molecular systematics has re-inforced Deuterostomia as a clade of bilaterian animals. Butmolecular evidence also indicates that some animal phyla withmembers that have deuterostome developmental features, in-cluding ectoprocts and brachiopods, are not in the deutero-stome dade (see Chapter 32). Hence, despite its name, the clade

chordatesdeuterostomes

! CmdanaLopholrochozoaEcdysozoaDeuterostomia

Madreporite. Watercan flow in or outof the water vascularsystem into thesurrounding waterthrough themadreporite.

The surface of a sea star iscovered by spines that helpdefend against predators, aswell as by small gills thatprovide gas exchange.

Each tube foot consists of a bulb-like ampulla and a podium (footportion). When the ampulla squeezes. water is forced into the podium,which expands and contacts the substrate. Adhesive chemicals are thensecreted from the base of the podium, attaching it to the substrate. Todetach the tube foot, de-adhesive chemicals are secreted and musclesin the podium contract, forcing water back into the ampulla andshortening the podium. As it moves, a sea star leaves an observableNfootprint H of adhesive material on the substrate.

Radial canal. The water vascularsystem consists of a ring canal in thecentral disk and five radial canals,each running in a groove down theentire length of an arm. Branchingfrom each radial canal are hundredsof hollow, muscular tube feet filledwith fluid.

Ashort digestive tract runs from themouth on the bottom of the centraldisk to the anus on top of the disk.

/

Central disk. The central diskrhas a nerve ring and nerve

cords radiating from the ringinto the arms.

Digestive glands secretedigestive juices and aid in the

absorption and storageof nutrients.

... Figure 33.39 Anatomy of a sea star, an echinoderm.

CHAPTER THIRTY·THREE Invertebrates 693

Tuesday, April 13, 2010

Biology II - Zoology

InvertebratesEchinodermata

(a) Asea star (class Asteroidea)

«) Asea urchin (class E(hinoidea)

(e) Asea cucumber (class Holothuroidea).. Figure 33.40 Echinoderms.

(b) Abrittle star (class Ophiuroidea)

(d) Afeather star (class Crinoidea)

(f) A sea daisy (class Con(entricycloidea)

1. Describe how sea star tube feet attach to substrates.2. Are characteristics shared by a sea star and a sea daisyhomologous or analogous? Explain.

3.•i,il:O'I,. The insectDrosophila me/anogaslerandthe nematode Caenurhabditis e/egans are prominentmodel organisms. Are these species the most appro-priate invertebrates for making inferences about hu-mans and other vertebrates in Deuterostomia? Explain.For suggested answers. see AppendiK A.

ChordalesPhylum Chordata consists ofm'o subphyla of invertebrates aswell as the hagfishes and the vertebrates. Chordates are bilat-erally symmetrical coelomates with segmented bodies. Thedose relationship between echinoderms and chordates doesnot mean that one phylum evolved from the other. In fact,echinoderms and chordates have evolved independently ofone another for at least 500 million years. We will trace thephylogeny ofchordates in Chapter 34, focusing on the historyof vertebrates.

CONCEPT CHECK 33.5

(HAPTER THIRTY·THREE Invertebrates 695

Echinoderms

Deuterostomia is defined primarily by DNA similarities-notdevelopmental similarities.

Sea stars and most other echinoderms (from the Greek echin,spiny, and derma, skin) are slow-moving or sessile marine an-imals. A thin epidermis covers an endoskeleton of hard cal-careous plates. Most echinoderms are prickly from skeletalbumps and spines. Unique to echinoderms is the watervascular system, a network ofhydraulic canals branching intoextensions called tube feet that function in locomotion, feed-ing, and gas exchange (Figure 33.39). Sexual reproduction ofechinoderms usually involves separate male and female indi-viduals that release their gametes into the water.The internal and external parts of most adult echinoderms

radiate from the center, often as five spokes. However, echin-oderm larvae have bilateral symmetry. Furthermore, the sym-metry of adult echinoderms is not truly radial. For example,the opening (madreporite) ofa sea star's water vascular systemis not central but shifted to one side.

are

Sea stars, sea urchins, and othere<hinoderms (phylumdermata) may seem to have lit-tle in common with phylumChordata, which includes the

vertebrates-animals that have a backbone. In fact, however,echinoderms and chordates share features characteristic of adeuterostome mode of development, such as radial cleavageand formation of the mouth at the end of the embryo oppositethe blastopore (see Figure 32.9). Molecular systematics has re-inforced Deuterostomia as a clade of bilaterian animals. Butmolecular evidence also indicates that some animal phyla withmembers that have deuterostome developmental features, in-cluding ectoprocts and brachiopods, are not in the deutero-stome dade (see Chapter 32). Hence, despite its name, the clade

chordatesdeuterostomes

! CmdanaLopholrochozoaEcdysozoaDeuterostomia

Madreporite. Watercan flow in or outof the water vascularsystem into thesurrounding waterthrough themadreporite.

The surface of a sea star iscovered by spines that helpdefend against predators, aswell as by small gills thatprovide gas exchange.

Each tube foot consists of a bulb-like ampulla and a podium (footportion). When the ampulla squeezes. water is forced into the podium,which expands and contacts the substrate. Adhesive chemicals are thensecreted from the base of the podium, attaching it to the substrate. Todetach the tube foot, de-adhesive chemicals are secreted and musclesin the podium contract, forcing water back into the ampulla andshortening the podium. As it moves, a sea star leaves an observableNfootprint H of adhesive material on the substrate.

Radial canal. The water vascularsystem consists of a ring canal in thecentral disk and five radial canals,each running in a groove down theentire length of an arm. Branchingfrom each radial canal are hundredsof hollow, muscular tube feet filledwith fluid.

Ashort digestive tract runs from themouth on the bottom of the centraldisk to the anus on top of the disk.

/

Central disk. The central diskrhas a nerve ring and nerve

cords radiating from the ringinto the arms.

Digestive glands secretedigestive juices and aid in the

absorption and storageof nutrients.

... Figure 33.39 Anatomy of a sea star, an echinoderm.

CHAPTER THIRTY·THREE Invertebrates 693

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

Echinoderms

Deuterostomia is defined primarily by DNA similarities-notdevelopmental similarities.

Sea stars and most other echinoderms (from the Greek echin,spiny, and derma, skin) are slow-moving or sessile marine an-imals. A thin epidermis covers an endoskeleton of hard cal-careous plates. Most echinoderms are prickly from skeletalbumps and spines. Unique to echinoderms is the watervascular system, a network ofhydraulic canals branching intoextensions called tube feet that function in locomotion, feed-ing, and gas exchange (Figure 33.39). Sexual reproduction ofechinoderms usually involves separate male and female indi-viduals that release their gametes into the water.The internal and external parts of most adult echinoderms

radiate from the center, often as five spokes. However, echin-oderm larvae have bilateral symmetry. Furthermore, the sym-metry of adult echinoderms is not truly radial. For example,the opening (madreporite) ofa sea star's water vascular systemis not central but shifted to one side.

are

Sea stars, sea urchins, and othere<hinoderms (phylumdermata) may seem to have lit-tle in common with phylumChordata, which includes the

vertebrates-animals that have a backbone. In fact, however,echinoderms and chordates share features characteristic of adeuterostome mode of development, such as radial cleavageand formation of the mouth at the end of the embryo oppositethe blastopore (see Figure 32.9). Molecular systematics has re-inforced Deuterostomia as a clade of bilaterian animals. Butmolecular evidence also indicates that some animal phyla withmembers that have deuterostome developmental features, in-cluding ectoprocts and brachiopods, are not in the deutero-stome dade (see Chapter 32). Hence, despite its name, the clade

chordatesdeuterostomes

! CmdanaLopholrochozoaEcdysozoaDeuterostomia

Madreporite. Watercan flow in or outof the water vascularsystem into thesurrounding waterthrough themadreporite.

The surface of a sea star iscovered by spines that helpdefend against predators, aswell as by small gills thatprovide gas exchange.

Each tube foot consists of a bulb-like ampulla and a podium (footportion). When the ampulla squeezes. water is forced into the podium,which expands and contacts the substrate. Adhesive chemicals are thensecreted from the base of the podium, attaching it to the substrate. Todetach the tube foot, de-adhesive chemicals are secreted and musclesin the podium contract, forcing water back into the ampulla andshortening the podium. As it moves, a sea star leaves an observableNfootprint H of adhesive material on the substrate.

Radial canal. The water vascularsystem consists of a ring canal in thecentral disk and five radial canals,each running in a groove down theentire length of an arm. Branchingfrom each radial canal are hundredsof hollow, muscular tube feet filledwith fluid.

Ashort digestive tract runs from themouth on the bottom of the centraldisk to the anus on top of the disk.

/

Central disk. The central diskrhas a nerve ring and nerve

cords radiating from the ringinto the arms.

Digestive glands secretedigestive juices and aid in the

absorption and storageof nutrients.

... Figure 33.39 Anatomy of a sea star, an echinoderm.

CHAPTER THIRTY·THREE Invertebrates 693

EchinodermataEchinoderms

Star-shaped body with multiple arms; mouth directed to substrateAsteroidea

Class and Examples

Ophiuridea Distinct central disk; long, flexible arms; incomplete digestive system

Echinoidea Roughly spherical or disk-shaped; no arms; five rows of tube feet, enabling slow movement; mouth ringed by complex, jaw-like structure

Feathered arms surrounding upward-pointing mouth; suspension feedersCrinoidea

Holothuroidea Cucumber-shaped body; five rows of tube feet; tube feet around the mouth are modified as feeding tentacles; reduced skeleton;no spines

Concentri-cycloidea

Armless, disk-shaped body ringed with small spines: incomplete digestive system; live on sub- merged wood

Main characteristics

Tuesday, April 13, 2010

Biology II - Zoology

Invertebrates

Echinoderms

Deuterostomia is defined primarily by DNA similarities-notdevelopmental similarities.

Sea stars and most other echinoderms (from the Greek echin,spiny, and derma, skin) are slow-moving or sessile marine an-imals. A thin epidermis covers an endoskeleton of hard cal-careous plates. Most echinoderms are prickly from skeletalbumps and spines. Unique to echinoderms is the watervascular system, a network ofhydraulic canals branching intoextensions called tube feet that function in locomotion, feed-ing, and gas exchange (Figure 33.39). Sexual reproduction ofechinoderms usually involves separate male and female indi-viduals that release their gametes into the water.The internal and external parts of most adult echinoderms

radiate from the center, often as five spokes. However, echin-oderm larvae have bilateral symmetry. Furthermore, the sym-metry of adult echinoderms is not truly radial. For example,the opening (madreporite) ofa sea star's water vascular systemis not central but shifted to one side.

are

Sea stars, sea urchins, and othere<hinoderms (phylumdermata) may seem to have lit-tle in common with phylumChordata, which includes the

vertebrates-animals that have a backbone. In fact, however,echinoderms and chordates share features characteristic of adeuterostome mode of development, such as radial cleavageand formation of the mouth at the end of the embryo oppositethe blastopore (see Figure 32.9). Molecular systematics has re-inforced Deuterostomia as a clade of bilaterian animals. Butmolecular evidence also indicates that some animal phyla withmembers that have deuterostome developmental features, in-cluding ectoprocts and brachiopods, are not in the deutero-stome dade (see Chapter 32). Hence, despite its name, the clade

chordatesdeuterostomes

! CmdanaLopholrochozoaEcdysozoaDeuterostomia

Madreporite. Watercan flow in or outof the water vascularsystem into thesurrounding waterthrough themadreporite.

The surface of a sea star iscovered by spines that helpdefend against predators, aswell as by small gills thatprovide gas exchange.

Each tube foot consists of a bulb-like ampulla and a podium (footportion). When the ampulla squeezes. water is forced into the podium,which expands and contacts the substrate. Adhesive chemicals are thensecreted from the base of the podium, attaching it to the substrate. Todetach the tube foot, de-adhesive chemicals are secreted and musclesin the podium contract, forcing water back into the ampulla andshortening the podium. As it moves, a sea star leaves an observableNfootprint H of adhesive material on the substrate.

Radial canal. The water vascularsystem consists of a ring canal in thecentral disk and five radial canals,each running in a groove down theentire length of an arm. Branchingfrom each radial canal are hundredsof hollow, muscular tube feet filledwith fluid.

Ashort digestive tract runs from themouth on the bottom of the centraldisk to the anus on top of the disk.

/

Central disk. The central diskrhas a nerve ring and nerve

cords radiating from the ringinto the arms.

Digestive glands secretedigestive juices and aid in the

absorption and storageof nutrients.

... Figure 33.39 Anatomy of a sea star, an echinoderm.

CHAPTER THIRTY·THREE Invertebrates 693

Sea star

Echinoderms

Deuterostomia is defined primarily by DNA similarities-notdevelopmental similarities.

Sea stars and most other echinoderms (from the Greek echin,spiny, and derma, skin) are slow-moving or sessile marine an-imals. A thin epidermis covers an endoskeleton of hard cal-careous plates. Most echinoderms are prickly from skeletalbumps and spines. Unique to echinoderms is the watervascular system, a network ofhydraulic canals branching intoextensions called tube feet that function in locomotion, feed-ing, and gas exchange (Figure 33.39). Sexual reproduction ofechinoderms usually involves separate male and female indi-viduals that release their gametes into the water.The internal and external parts of most adult echinoderms

radiate from the center, often as five spokes. However, echin-oderm larvae have bilateral symmetry. Furthermore, the sym-metry of adult echinoderms is not truly radial. For example,the opening (madreporite) ofa sea star's water vascular systemis not central but shifted to one side.

are

Sea stars, sea urchins, and othere<hinoderms (phylumdermata) may seem to have lit-tle in common with phylumChordata, which includes the

vertebrates-animals that have a backbone. In fact, however,echinoderms and chordates share features characteristic of adeuterostome mode of development, such as radial cleavageand formation of the mouth at the end of the embryo oppositethe blastopore (see Figure 32.9). Molecular systematics has re-inforced Deuterostomia as a clade of bilaterian animals. Butmolecular evidence also indicates that some animal phyla withmembers that have deuterostome developmental features, in-cluding ectoprocts and brachiopods, are not in the deutero-stome dade (see Chapter 32). Hence, despite its name, the clade

chordatesdeuterostomes

! CmdanaLopholrochozoaEcdysozoaDeuterostomia

Madreporite. Watercan flow in or outof the water vascularsystem into thesurrounding waterthrough themadreporite.

The surface of a sea star iscovered by spines that helpdefend against predators, aswell as by small gills thatprovide gas exchange.

Each tube foot consists of a bulb-like ampulla and a podium (footportion). When the ampulla squeezes. water is forced into the podium,which expands and contacts the substrate. Adhesive chemicals are thensecreted from the base of the podium, attaching it to the substrate. Todetach the tube foot, de-adhesive chemicals are secreted and musclesin the podium contract, forcing water back into the ampulla andshortening the podium. As it moves, a sea star leaves an observableNfootprint H of adhesive material on the substrate.

Radial canal. The water vascularsystem consists of a ring canal in thecentral disk and five radial canals,each running in a groove down theentire length of an arm. Branchingfrom each radial canal are hundredsof hollow, muscular tube feet filledwith fluid.

Ashort digestive tract runs from themouth on the bottom of the centraldisk to the anus on top of the disk.

/

Central disk. The central diskrhas a nerve ring and nerve

cords radiating from the ringinto the arms.

Digestive glands secretedigestive juices and aid in the

absorption and storageof nutrients.

... Figure 33.39 Anatomy of a sea star, an echinoderm.

CHAPTER THIRTY·THREE Invertebrates 693

Echinoderms

Tuesday, April 13, 2010

Biology II - Zoology

InvertebratesChordates

Chordates are bilaterally symmetrical coelomates with segmented bodies. The close relationship between echinoderms and chordates does not mean that one phylum evolved from the other. In fact, echinoderms and chordates have evolved independently of one another for at least 500 million years.

Echinoderms

Deuterostomia is defined primarily by DNA similarities-notdevelopmental similarities.

Sea stars and most other echinoderms (from the Greek echin,spiny, and derma, skin) are slow-moving or sessile marine an-imals. A thin epidermis covers an endoskeleton of hard cal-careous plates. Most echinoderms are prickly from skeletalbumps and spines. Unique to echinoderms is the watervascular system, a network ofhydraulic canals branching intoextensions called tube feet that function in locomotion, feed-ing, and gas exchange (Figure 33.39). Sexual reproduction ofechinoderms usually involves separate male and female indi-viduals that release their gametes into the water.The internal and external parts of most adult echinoderms

radiate from the center, often as five spokes. However, echin-oderm larvae have bilateral symmetry. Furthermore, the sym-metry of adult echinoderms is not truly radial. For example,the opening (madreporite) ofa sea star's water vascular systemis not central but shifted to one side.

are

Sea stars, sea urchins, and othere<hinoderms (phylumdermata) may seem to have lit-tle in common with phylumChordata, which includes the

vertebrates-animals that have a backbone. In fact, however,echinoderms and chordates share features characteristic of adeuterostome mode of development, such as radial cleavageand formation of the mouth at the end of the embryo oppositethe blastopore (see Figure 32.9). Molecular systematics has re-inforced Deuterostomia as a clade of bilaterian animals. Butmolecular evidence also indicates that some animal phyla withmembers that have deuterostome developmental features, in-cluding ectoprocts and brachiopods, are not in the deutero-stome dade (see Chapter 32). Hence, despite its name, the clade

chordatesdeuterostomes

! CmdanaLopholrochozoaEcdysozoaDeuterostomia

Madreporite. Watercan flow in or outof the water vascularsystem into thesurrounding waterthrough themadreporite.

The surface of a sea star iscovered by spines that helpdefend against predators, aswell as by small gills thatprovide gas exchange.

Each tube foot consists of a bulb-like ampulla and a podium (footportion). When the ampulla squeezes. water is forced into the podium,which expands and contacts the substrate. Adhesive chemicals are thensecreted from the base of the podium, attaching it to the substrate. Todetach the tube foot, de-adhesive chemicals are secreted and musclesin the podium contract, forcing water back into the ampulla andshortening the podium. As it moves, a sea star leaves an observableNfootprint H of adhesive material on the substrate.

Radial canal. The water vascularsystem consists of a ring canal in thecentral disk and five radial canals,each running in a groove down theentire length of an arm. Branchingfrom each radial canal are hundredsof hollow, muscular tube feet filledwith fluid.

Ashort digestive tract runs from themouth on the bottom of the centraldisk to the anus on top of the disk.

/

Central disk. The central diskrhas a nerve ring and nerve

cords radiating from the ringinto the arms.

Digestive glands secretedigestive juices and aid in the

absorption and storageof nutrients.

... Figure 33.39 Anatomy of a sea star, an echinoderm.

CHAPTER THIRTY·THREE Invertebrates 693

Tuesday, April 13, 2010

Biology II - Zoology

Chordates

9oa•

,•

•!••3,o·;•Mammalia

(mammals)

Actinopterygii ..-....(ray·finned fishes)

Chondrichthyes(sharks. rays, chimaeras) "..",.,..

Actinistia ..(coelacanths) ..

Petromyzontida(lampreys)

Cephalochordata(Iancelets)

Echinodermata(sister group to chordates)

Myxini(haglishes)

Urochordata(tunicates)

Dipnoi

Amphibiasalamanders) '.-QReptilia _(turtles. snakes,crocodiles. birds)

Milk

-OMENot"h;Commonancestor of -chordates

H:tVertebral COI±

Jaws. mineralized skel±

lungs or lung deriva±

-.2 Phylogeny of living chordates. This :t -hypothesis shows the major clades of chordates inother main deuterostome clade. Echinodermata (see

Am"ioti''j; +For selected clades. some 01 the derived charactersexample. all chordates. and only chordates. have

ANCESTRALDEUTEROST

.. Figure 34phylogeneticrelation to theChapter 33).are listed; fora notochord.

to vertebrates than to other invertebrates. Along with the hag-fishes and the vertebrates, they make up the chordates.

Derived Characters of ChordatesAll chordates share a set ofderived characters, though manyspecies possess some of these traits only during embryonicdevelopment. Figure 34.3 illustrates four key characters ofchordates: a notochord; a dorsal, hollow nerve cord; pharyn-geal slits or clefts; and a muscular, post-anal tail.

Musclesegments

Mu5tular,post-anal tail

Dorsal,hollownerve cord

Notochord

Anus Pharyngealslits or clefts

Notochord

Chordates are named for a skeletal structure, the notochord,present in all chordate embryos as well as in some adult chor-dates. The notochord is a longitudinal, flexible rod locatedbehveen the digestive tube and the nerve cord. It is composedof large, fluid-filled cells encased in fairly stiff, fibrous tissue.TIle notochord provides skeletal support throughout most ofthe length of a chordate, and in larvae or adults that retain it,it also provides a firm but flexible structure against which

.4 Figure 34.3 Chordate characteristics. All chordates possessthe lour highlighted structural trademarks at some point during theirdevelopment.

muscles can work during swimming. In most vertebrates, amore complex, jointed skeleton develops around the ancestralnotochord, and the adult retains only remnants of the embry-onic notochord. In humans, the notochord is reduced to gel-atinous disks sandwiched between the vertebrae.

(IlP,PTH TIlIRTY·fOUR Vertebrates 699

Echinodermata. For selected clades, some of the derived characters are listed; for example all chordates, and only chordates, have a notochord.

Phylogeny of living chordates. This phylogenetic hypothesis shows the major clades of chordates in relation to the other main deuterostome clade,

Echinoderms

Deuterostomia is defined primarily by DNA similarities-notdevelopmental similarities.

Sea stars and most other echinoderms (from the Greek echin,spiny, and derma, skin) are slow-moving or sessile marine an-imals. A thin epidermis covers an endoskeleton of hard cal-careous plates. Most echinoderms are prickly from skeletalbumps and spines. Unique to echinoderms is the watervascular system, a network ofhydraulic canals branching intoextensions called tube feet that function in locomotion, feed-ing, and gas exchange (Figure 33.39). Sexual reproduction ofechinoderms usually involves separate male and female indi-viduals that release their gametes into the water.The internal and external parts of most adult echinoderms

radiate from the center, often as five spokes. However, echin-oderm larvae have bilateral symmetry. Furthermore, the sym-metry of adult echinoderms is not truly radial. For example,the opening (madreporite) ofa sea star's water vascular systemis not central but shifted to one side.

are

Sea stars, sea urchins, and othere<hinoderms (phylumdermata) may seem to have lit-tle in common with phylumChordata, which includes the

vertebrates-animals that have a backbone. In fact, however,echinoderms and chordates share features characteristic of adeuterostome mode of development, such as radial cleavageand formation of the mouth at the end of the embryo oppositethe blastopore (see Figure 32.9). Molecular systematics has re-inforced Deuterostomia as a clade of bilaterian animals. Butmolecular evidence also indicates that some animal phyla withmembers that have deuterostome developmental features, in-cluding ectoprocts and brachiopods, are not in the deutero-stome dade (see Chapter 32). Hence, despite its name, the clade

chordatesdeuterostomes

! CmdanaLopholrochozoaEcdysozoaDeuterostomia

Madreporite. Watercan flow in or outof the water vascularsystem into thesurrounding waterthrough themadreporite.

The surface of a sea star iscovered by spines that helpdefend against predators, aswell as by small gills thatprovide gas exchange.

Each tube foot consists of a bulb-like ampulla and a podium (footportion). When the ampulla squeezes. water is forced into the podium,which expands and contacts the substrate. Adhesive chemicals are thensecreted from the base of the podium, attaching it to the substrate. Todetach the tube foot, de-adhesive chemicals are secreted and musclesin the podium contract, forcing water back into the ampulla andshortening the podium. As it moves, a sea star leaves an observableNfootprint H of adhesive material on the substrate.

Radial canal. The water vascularsystem consists of a ring canal in thecentral disk and five radial canals,each running in a groove down theentire length of an arm. Branchingfrom each radial canal are hundredsof hollow, muscular tube feet filledwith fluid.

Ashort digestive tract runs from themouth on the bottom of the centraldisk to the anus on top of the disk.

/

Central disk. The central diskrhas a nerve ring and nerve

cords radiating from the ringinto the arms.

Digestive glands secretedigestive juices and aid in the

absorption and storageof nutrients.

... Figure 33.39 Anatomy of a sea star, an echinoderm.

CHAPTER THIRTY·THREE Invertebrates 693

Tuesday, April 13, 2010