Worms and Mollusks

Worms and MollusksChapter 27:

1. Flatworms (phylum Platyhelminthes)Turbellaria (free-living)Trematoda (flukes), Cestoda (tape worms)

2. Round Worms (phylum Nematoda)Trichinella (trichinosis)filarial worms (elephantiasis) Ascaris and hookworms

3. Segmented Worms (phylum Annelida)Oligochaeta (earthworms) Hyrudinea (leeches) Polychaeta (sandworms, bloodworms)

3 Phylums of Worms

1. belly-footed (class Gastropoda)“gastro means belly & pod means foot”snails and slugs

2. double-shelled (class Bivalvia)“bi means 2 & valve means shell”clams,mussels, oysters and scallops

3. head-footed (class Cephalopoda)“cephalo means head & pod means foot” octopus, squid, cuddlefish, nautilus

Classes of Mollusca Phylum

“No Coelum”

“True Coelum”

“False Coelum”

“Coelum - fluid filled body cavity line with tissue from mesoderm”

FLATWORMS

Flatworms• Phylum Platyhelminthes

• Soft, flattened animals with cephalization and bilateral symmetry

• Acoelomates: 3 germ layers with no true body cavity (coelom)

• Most are parasitic

• Terms: pharynx, flame cells, ganglia, hermaphodite

• Sexual and asexual reproduction

• Examples: flukes, planaria, tapeworms

• Acoelomate: flatworms are without a coelom

• Coelom: fluid-filled body cavity lined with mesoderm

• The digestive cavity is the only body cavity

Flatworms

Platyhelminthes Feeding• Free-living flatworms

– Carnivores that feed on tiny aquatic animals

– Scavengers that feed on recently dead animals

• Parasitic flatworms

– Feed on blood, tissue fluids, or pieces of cells within a host’s body (Example: tapeworm)

Respiration, Circulation, & Excretion in Platyhelminthes

• Rely on diffusion

• Flame cells: remove excess water and metabolic wastes from the body

Platyhelminthes Response

• Ganglia: group of nerve cells that controls the nervous system; in the head region

• Eyespot

Platyhelminthes Movement

• Cilia

• Muscle cells

• Flap to swim

Reproduction: Sexually and Asexually in Platyhelminthes

Free-living

• Sexually: hermaphrodites

during sexual reproduction, two worms join in a pair, delivering sperm to each other

• Asexually: fission

Reproduction: Sexually and Asexually in Platyhelminthes

Parasitic

• A complex life cycle including both sexual and asexual reproduction

Groups of Flatworms: Platyhelminthes

• Flukes - parasitic; infect the internal organs of their host (class Trematoda)

•Tapeworms - Long, flat, parasitic; adapted to life inside the intestines of their host (class Cestoda)

•Turbellarians - free-living; most live in marine or fresh water (class Terbellaria)

• Free living Flatworms

• Most live in freshwater or marine environments

• Bottom dwellers living in sand or mud

• Most are carnivores or detritus

• Example: Planarians

Groups of Flatworms: Platyhelminthes Class: Turbellarians

• Parasitic Flatworms• Most flukes infect the internal organs of their host• Some are external parasites that live on the skin,

mouth, gills of their host• Many have complicated life cycles that involve two

or more animal hosts• They are usually less than a centimeter long• They cause serious pain to millions of humans and

animals• The most destructive live in the tropics.

Groups of Flatworms: Platyhelminthes Class: Trematoda (Flukes)

Liver Fluke Life Cycle

•

• Flukes of the genus Schistosoma infect about 200 million people per year

• The Schistosoma fluke causes schistosomiasis in humans

• A serious disease in which the eggs clog blood vessels which can cause swelling and tissue decay in the lungs, liver, spleen, or intestines

Groups of Flatworms: Platyhelminthes Class: Trematoda (Flukes)

Blood Flukes

• Larvae enter humans through skin

• Reproduce sexually in blood vessels of intestines

• Release eggs into water

• Larvae enter snails and reproduce asexually

• Burrow out and infect humans again

– More prevalent with no sewage treatment

Groups of Flatworms: Platyhelminthes Life Cycle of Schistosoma

Blood Fluke Life Cycle

•

• Parasitic worms

• Adapted to live inside the intestines of their hosts

• Food is digested directly through the body walls

• Rarely kill but cause weakness & weight loss

Groups of Flatworms: PlatyhelminthesClass: Cestoda (tapeworms)

• Structure of a tapeworm

• Scolex– Structure that contains suckers or hooks

Groups of Flatworms: PlatyhelminthesClass: Cestoda (tapeworms)

• Proglottids– Segments that make up most of the worms body– Proglottids contain male and female reproductive parts – They can contain as many as 100,000 eggs.– They can produce as many as half a billion eggs in a

year

Groups of Flatworms: PlatyhelminthesClass: Cestoda (tapeworms)

Tapeworm Life Cycle

• Taenia saginata, the Beef Tapeworm

Groups of Flatworms: PlatyhelminthesClass: Cestoda (tapeworms)

ROUNDWORMS

Roundworms• Phylum Nematoda• No segments• Many free-living, some Parasitic• Pseudocoelomate: 3 germ layers

with false cavity(coelom)• Digestive system with two

openings: mouth and anus• Inhabit the soil, salt flats, aquatic

sediments and water from polar regions to the tropics

• Hookworms, trichinella, ascaris“A rotting apple may contain 100,000 nematodes!”

Roundworms

Nematode Feeding

Carnivores that use grasping mouth parts and spines

Free-living roundworms

Respiration, Circulation, & Excretion in Nematodes

• Exchange gases and excrete metabolic waste through their body walls

• No internal transport system

• They rely on diffusion to carry nutrients and waste throughout their bodies

Nematode Response• Simple nervous systems, consisting of

several ganglia

• Run from the head to the tail

• Nerves transmit sensory information and control movement

Nematode Movement

• Hydrostatic skeleton

• Aquatic roundworms move like snakes

• Soil-dwelling roundworms push their way through by thrashing around

Nematode Reproduction

• Sexually

• Separate males and females

• Internal fertilization

• Male deposits sperm inside the female’s reproductive tract

• Parasitic roundworms have complex life cycles involving two or three different hosts or organs within a single host

Nematode Reproduction

Roundworms and Human DiseaseTrichinosis-causing worms

• Adult worms live and mate in the intestines of their host (humans, pigs and other mammals)

Filarial worms

• Found primarily in tropical regions of Asia, threadlike worms that live in the blood and lymph vessels of birds and mammals, including humans, transmitted by biting insects, causes elephantiasis

Roundworms and Human DiseaseAscarid worms

• Serious parasite of humans and many other vertebrates, causes malnutrition; spread by eating vegetables or food that are not washed properly

Hookworms

• Hatch outside the body of the host and develop in the soil, can enter a barefoot and travel through the bloodstream to the intestines

Roundworms Causing Human Disease:Trichinosis - Causing Worms

• Trichinosis is a terrible disease caused by the roundworm Trichinella

• Adult worms live and mate in the intestines of their hosts which include:

– Humans, pigs, and other animals

Warning… Very Graphic Images! (next 11 slides)

Roundworms Causing Human Disease: Trichinella Worm - Trichinosis

Humans get Trichinosis by eating raw or incompletely

cooked pork.

Roundworms Causing Human Disease: Filarial Worms

• Found primarily in tropical regions of Asia

• Threadlike worms live in blood and lymph vessels of birds and mammals…including humans

• Transmitted through bitting insects especially mosquitos

• Large numbers of filarial worms may block the passage of fluids within the lymph vessels

• This causes what is known as elephantiasis

Roundworms Causing Human Disease: Filarial Worms - Elephantiasis

• Ascaris lumbricoides is a serious parasite of humans and other vertebrate animals

• Causes malnutrition to more than 1 billion people worldwide including many people living in the southeastern United States

– Cause: by eating vegetables and other foods that are not washed properly

Roundworms Causing Human Disease: Ascarid Worms

Roundworms Causing Human Disease: Ascarid Worms

This is why we have to

have puppies “wormed” Ascarids

affect many other animals

Video: Worms in a dog’s heart

Roundworms Causing Human Disease: Ascarid Worms

Roundworms Causing Human Disease: Hookworms

• As many as one quarter of the people in the world are infected with hookworms

• They suck the hosts blood causing weakness and poor growth

• See chart for life cycle!

Roundworms Causing Human Disease: Hookworms

Roundworms Causing Human Disease: Hookworms

•

Roundworms Causing Human Disease: New Guinea Worms

Research on C. elegans

• Free-living roundworm Caenorhabditis elegans, C. elegans

• Feeds on rotting vegetation

• First multicellular animal whose DNA was fully sequenced

• Helps understand genes and how eukaryotes became multicellular

ANNELIDS

Segmented Worms

• Phylum Annelida

• Annelid means “little ring”

• True coelom coelomates

• Embryonic similarity to mollusks because of larval stage called trocophore

• Ecology: aeration of soils, castings increase nutrients in soil, food source

Annelids• True coelom that is lined

• Segmented bodies

• Septa: internal walls between each segment

• Setae: bristles that are attached to each segment; used in respiration

Form and Function in Annelids

• Have complex organ systems

• Segmented body

Form and Function in Annelids

Annelid Feeding and Digestion

• Filter feeders to predators

• Get their food using a pharynx

• Crop: in earthworms; part of the digestive system in which food can be stored

• Gizzard: in earthworms; part of the digestive system in which food is ground into smaller pieces

Annelid Circulation• Closed circulatory system: blood is contained within

a network of blood vessels

• Blood circulates through two major blood vessels that run from head to tail

• Blood in dorsal vessel moves blood toward the head of the worm

• Blood in ventral vessel runs from head to tail

• Dorsal blood vessel functions like a heart because it contracts and helps pump blood

Annelid Respiration

• Aquatic annelids: gills

• Land-dwelling annelids: diffusion through their moist skin

Annelid Excretion

• Two kinds of waste (digestive & nitrogen)

1. Digestive waste passes out through the anus at the end of the digestive tract

2. Nephridia: excretory organs that filter fluid in the coelom (nitriogen waste)

Annelid Response• Well-developed nervous system consisting

of a brain and several nerve cords

• The sense organs are best developed in free-living marine annelids

• Also have adaptations for detecting stimuli

• Sensory tentacles• Chemical receptors• Statocysts (help to detect gravity)• Two or more pair of eyes

Annelid Movement

• Hydrostatic skeleton

• Longitudinal muscles and circular muscles

• Moves by alternating contracting these two sets of muscles

• Sexually, external fertilization or have separate sexes

• Earthworms and leeches are hermaphroditic

– Exchange sperm • Seminal vesicles – produce sperm• Seminal receptacles – receive sperm

– Clitellum: a band of thickened, specialized segments that secretes a mucus ring into which eggs and sperm are released and fertilization occurs

– The ring slips off the body and form a protective cocoon for the worms that hatch a week later

Annelid Reproduction

Annelid Reproduction

Annelid Reproduction

Groups of Annelids• Class Oligochaetes (Ahl-il-goh-keets) earthworms

– streamlined and have relatively few setae compared to polychaetes, live in soil or water

• Class Hirudinea (hir-yoo-DIN-ee-uh) leeches– External parasites that suck the blood and body fluids

of their host

• Class Polychaeta (pahl-ih-keets) sand and bloodworms– Marine annelids that have paired, paddlelike

appendages tipped with setae

• Earthworms

– Annelids that have few setae

– Live in soil or fresh water

– Spend most of lives hidden underground

• Can see evidence of an earthworm above ground in CASTINGS

– Castings: Indigestible particles of sand, clay, and grains that are passed out of the worm through the anus

Groups of Segmented: Annelida Class: Oligochaeta

Anus

Clitellum

Circular muscle

Longitudinalmuscle

Nephridia Ganglia Ringvessels

Reproductiveorgans

Ventralblood vessel

Ganglion

Brain

Mouth

Dorsalblood vessel

CropGizzardBody segments

Setae

Groups of Segmented: Annelida Class: Oligochaeta

• Leeches– Live in moist, tropical countries– External parasites that suck the blood

and body fluids of their host– Have powerful suckers at both ends of their bodies– Leeches are sometimes used after surgery

• Can reduce swelling when a body part is reattached

• Also secrete a fluid that prevents blood from clotting

• They can suck up to five times their weight in blood!

Groups of Segmented: Annelida Class: Hirudinea

MEDICALLEECHES

LEECHSUCKERS

• Sandworms, Bloodworms– Marine annelids that have paired, paddle-like

appendages tipped with setae– Live in cracks in coral reefs, in sand, mud or open

water

Groups of Segmented: Annelida Class: Polychaeta

FANWORMS

Groups of Segmented: Annelida Class: Polychaeta

Groups of Segmented: Annelida Class: Polychaeta

SANDWORMS

Ecology of Annelids• Provide passageways for plant roots and

water and allow the growth of beneficial, oxygen requiring soil bacteria

• Important in the diet of many birds, moles, skunks, toads and snakes

• In the sea they participate in a wide range of food chains

MOLLUSKS

• Soft-bodied with internal or external shell

• Foot, mantle, visceral mass, shell• Uses a radula to feed• Water enters and leaves through a

siphon• Gastropods: snails and slugs• Bivalves: clams, mussels, scallops• Cephalopods: squid, octopi, • Food source, research, filter-feeders

Mollusks

•Trochophore: free-swimming larval stage of aquatic mollusk

• All seem very different, but grouped together because they share very similar developmental stages– Aquatic mollusks have free-swimming larval stage

called trochophore

Mollusks

Form and Function in Mollusks

• True coeloms

• Have complex organ systems

Mollusk Body Plan

• Foot: muscular part of a mollusk

• Mantle: thin layer of tissue that covers most of a mollusk’s body

Mollusk Body Plan

• Shell: structure in mollusks made by glands in the mantle that secrete calcium carbonate

• Visceral mass: area beneath the mantle of a mollusk that contains the internal organs

Snail

Earlymollusk

Clam

Squid

Shell

Mantle cavity

Foot

Gills

Digestive

tract

Mollusk Body Plan

Mollusk Feeding• Herbivorous• Carnivores • Filter feeders• Detritivores• Parasites

• Radula: flexible, tongue-shaped structure used to capture food by snails and slugs

• Siphon: tube-like structure through which water enters and leaves the body, capturing plankton in the process

Mollusk Feeding

Octopi and some sea slugs use sharp jaws to eat prey

To subdue prey, some octopi also produce

poison

Mollusk Feeding

Clams and oysters filter feed using feathery gills

Draw in water using their SIPHON

Mollusk Respiration

• Gills inside their mantle cavity

• Land snails respire using a mantle cavity lined with blood vessels

• Typically live in moist places to keep this lining wet

Mollusk Circulation• Open circulatory system: blood is pumped through

vessels by a simple heart

– Works well for slow-moving mollusks such as snails and clams (demands for oxygen are low)

– Blood passes from sinuses to the gills, where they exchange O2 and CO2 and back to heart

• Closed circulatory system: can transport blood through an animal’s body much more quickly

Mollusk Excretion

• Cells of the body release nitrogen-containing waste into the blood in the form of ammonia

• Nephridia remove ammonia from the blood and release it out of the body

Mollusk Response

• Complexity of the nervous system varies greatly between mollusks

• Clams and other two-shelled mollusk lead inactive lives simple nervous system

Mollusk Response

• Octopi and their relatives are active and intelligent predators most highly developed nervous system of all invertebrates

• Capable of complex behavior, such as opening a jar to get food inside

Mollusk Movement

• Move in many different speeds

• Snails secrete mucus and move slowly over the surface using a rippling motion of the foot

• Torsion – twist guts into bag

• Octopus uses a form of jet propulsion, drawing water into its mantle and forcing it out the siphon (octopus squirts bird)

Mollusk Reproduction• Reproduce in many different ways• Most have separate males and

females (octopi hatch from eggs)• Snails and two-shelled mollusk

reproduce sexually by external fertilization

• octopi and squid reproduce sexually by internal fertilization

• Fertilized egg develops into free swimming trochophore larva

• Some mollusk are hermaphrodites

Groups of Mollusks• Gastropods (belly footed)

– Shell-less or single-shelled mollusks that move by using a muscular foot located on the ventral side

– Ex: snails, slugs, sea butterflies, nudibranchs, and conch

• Bivalves (2 shells)– Have two shells that are held together by powerful muscles– Ex: clams, oysters, mussels and scallops

• Cephalopods (head footed)– Soft-bodied mollusks in which the head is attached to a single foot;

the foot is divided into tentacles or arms– Ex: octopi, squids, cuttlefishes and nautiluses

Groups of Mollusks: class Gastropoda

Slugs!

Groups of Mollusks: class Gastropoda

Snail

Groups of Mollusks: class Gastropoda

Sea Slug

Groups of Mollusks: class Gastropoda

Conche

Groups of Mollusks: class Bivalve

Groups of Mollusks: class Bivalve

Groups of Mollusks: class Bivalve

Giant Clam

Groups of Mollusks: class Cephalopoda

Squid

Groups of Mollusks: class Cephalopoda

Caribbean Octopus

Groups of Mollusks: class Cephalopoda

Squid

Groups of Mollusks: class Cephalopoda

White Horned Octopus

Groups of Mollusks: class Cephalopoda

Sea Butterfly

Groups of Mollusks: class Gastropoda

Cuddlefish

Groups of Mollusks: class Cephalopoda

Groups of Mollusks: class Cephalopoda

Ecology of Mollusks

• Feed on plants, prey on animals, and clean up their environment by filtering algae out of the water or by eating detritus

• Filter-feeding bivalves can be used to monitor water quality

• Serve as subjects of biological research