Dawn of the Arthropods: An Introduction to 85%
Jan 20, 2016
Dawn of the Arthropods:An Introduction to 85%
The Arthropods
• First arthropods Early Cambrian 600 mya– All environments, diverse ecologies – Tiny mites + crustacea < 1 mm --- Japanese
spider crabs 3 m long – 85% of described animal taxa– 3 - 100 million species
Tardigrades and Onychophorans
Similar to Arthropods• chitinous cuticles
Phylum Tardigrada
• ~900 species• 50 – 1200 µm•Surface films of freshwater on terrestrial plants, mosses and lichens•abundant (3 million m-2)
Phylum Tardigrada
Defining characteristic: mouthparts: protrusible, oral stylet for piercing plant and animal tissues to obtain fluids
Phylum Tardigrada
• chitinous cuticle lining outer surface and gut• arthropod-like striated muscles• hemocoel• gas exchange across body surface
• NO RESPIRATORY STRUCTURES• lack cilia• 4 pairs of clawed appendages (non-jointed)
Phylum Tardigrada• nervous system similar to arthropods
• paired ventral nerve cord
• offspring develop as miniature adults • male deposits sperm into female seminal receptacle• cuticle never calcified• cryptobiosis – dehydrate with environmental extremes• gonochoristic•ANABIOSIS: reduced metabolism •CRYPTOBIOSIS: extreme anabiosis
video
Phylum Tardigrada
Phylum Onychophora“velvet worms”
Defining Characteristics:•2nd pair of appendages modified into jaws•3rd pair of appendages form oral papillae
Phylum Onychophora“velvet worms”
Defining Characteristics:•slime glands discharge adhesive through oral papillae•hydrostatic skeleton
Phylum Onychophora
• ~ 100 species • moist terrestrial habitat • thin, non-waxy cuticle• nocturnal
Phylum Onychophora
• carnivores, herbivores, omnivores• predators shoot proteinaceaous glue from oral papillae• some use glue as defense
video
Phylum Onychophora
• circular, longitudinal, and diagonal muscles• 1 pair feeding appendages• no jointed appendages• hydrostatic skeleton• pair of nephridia / segments
• Ocelli; no compound eyes, photonegative• Sperm morphology similar to oligochaetes and leeches•Mostly dioecious •Oviparous, viviparous, or ovoviviparous•Direct development
Phylum Onychophora
Phylum Arthropoda
• 6 classes• 80 orders
• 2400 families
• Loss of motile cilia
• Segmented, jointed, sclerotized chitinous exoskeleton
• Flexible joints, hemocoel, Sense organs, ecdysis, specialized segments (head, thorax, abdomen)
Phylum Arthropoda: Pechenik Classification
Subphyla:1)Trilobitomorpha (extinct)
1) Class Trilobita2)Chelicerata
1) Class Merostomata2) Class Arachnida3) Class Pycnogonida4) Class Eurypterida (extinct)
3)Mandibulata1) Class Myriapoda
1) Order Chilopoda/Diplopoda2) Class Hexapoda
1) Subclass Entognatha2) Subclass Insecta
3) Class Crustacea
Arthropoda Exoskeleton• water impermeable• procuticle – mostly chitin•EXOSKELETON LIMITS CONSTANT GROWTH
Arthropoda: Support and Locomotion• exoskeleton• Muscles connect body
segments + joints
• Exoskeleton across joints NOT absent, but thin and flexible;
Phylum Arthropoda
• metamerism• most taxa have fused and modified specialized segments
Molting
• exoskeleton covering except for sensory hairs, gland openings, spiracles• parts of gut also lined with cuticle• ecdysis – loss of exoskeleton
Molting
• new cuticle secreted first, but then hardened• period of vulnerability• under neural and hormonal control
Arthropoda Nervous System and Sense Organs
• Brain • Tactile receptors = bristles or setae
Arthropoda Nervous System and Sense Organs
• Brain • Tactile receptors = bristles or setae• Proprioception necessary with jointed appendages• Stretch receptors span joints and provide knowledge of limb
positions
Arthropoda Nervous System and Sense Organs
• Brain • Tactile receptors = bristles or setae• Proprioception necessary with jointed appendages• Stretch receptors span joints and provide knowledge of limb
positions• Three photoreceptors: simple ocelli, complex lensed ocelli,
compound eyes• Compound eyes: ommitidia• Ommitidium: nerve tracts and field of vision• Visual fields of neighboring ommitidia overlap
– movements detected by each– compound eyes suitable for detection of subtle movement
Arthropoda Nervous System and Sense Organs
• Brain • Tactile receptors = bristles or setae• Proprioception necessary with jointed appendages• Stretch receptors span joints and provide knowledge of limb
positions• Three photoreceptors: simple ocelli, complex lensed ocelli,
compound eyes• Compound eyes: ommitidia• Ommitidium: nerve tracts and field of vision• Visual fields of neighboring ommitidia overlap
– movements detected by each– compound eyes suitable for detection of subtle movement
Visual System
• ocelli or compound eyes• light sensitive surface with light-absorbing pigment
Circulation and Gas Exchange
• Gas exchange structures = invaginations in cuticle
• Inwardly branching trachea: hemocoel via spiracles
• gas exchange with hemolymph
Circulatory System
• heart with ostia = open circulatory system• hemolymph
Arthropoda Digestive System
• Foregut- ingestion, transport, storage, mechanical digestion
• Midgut- enzyme production, chemical digestion, absorption
• Hindgut- water absorption, preparation of fecal material
Arthropoda Excretion and Osmoregulation
• Nephridia and malpighian tubules• nephridial pores excrete concentrated nitrogenous waste
products• Urine from malpighian tubules to gut, concentrates urine
(reabsorb water)• Terrestrial arachnids, myriapods, and insects excrete
predominantly uric acid
Arthropoda Repro and Development
• Dioecious • Fertilization internal, parental care common
Class Trilobita
• 4000 described species• extinct• dorsoventrally flattened• 3 sections• biramous appendages
Crustacea
• Terrestrial and aquatic
• All depths in marine, brackish, and freshwater
• > 67,000 described species, likely 5-10x that number• Diverse form, size, and habitat• 5 classes, 34 orders
Crustacea
Subclass Malacostraca - Order Isopoda (pillbugs) - Order Amphipoda (scuds) - Order Euphausiacea (krill) - Order Stomatopoda - Order Decapoda (crabs, shrimp, lobsters, hermit crabs, crayfish)
Subclass Branchiopoda – brine (monkeys)Subclass Ostracoda - ostracodsSubclass Copepoda – copepodsSubclass Pentastomida – nasal parasites Subclass Cirripedia (maxilopoda) – barnacles
Characteristics
• Head = 5 segments, trunk divided into thorax and abdomen
• Carapace or cephalic shield• Appendages multi-articulate; either uniramous
or biramous• Mandibles are modified limbs that function as
jaws• Gas exchange by diffusion across specialized
surfaces
Characteristics
• Nephridia• Simple and compound eyes in at least one
stage– Compound eyes on stalk
• Gut with digestive cecae• Nauplius larvae, either mixed or direct
development• 2 pair antennae
Crustacean Bauplan
• Thorax– anterior segments fused = cephalon
• Maxillipeds: additional mouthparts• Number of segments in thorax varies • Thorax appendages = pereopods
– swimming, walking, gas exchange, feeding, defense– ultiarticulate and biramous
Basic Crustacean Bauplan
• Abdomen– Segments – Number of segments used in ID
• Appendages = pleopods– Biramous, flap-like– swimming
– Culminate in telson• Anus• caudal rami• w/uropods (last pair of abdominal appendages) forms tail
fan
Adult Crustacean
Crustacean Bauplan
• Nauplius Larvae– Single, median, simple eye– 3 pairs of sectioned, functional limbs
• Become antennules, antennae, and mandibles
Circulation
• Open circulatory system– Dorsal ostiate heart– Internal organs bathed in fluid– Simple heart and vessels in most
• Sessile species no heart; pumping vessels
• Blood– Variety of cell types
• Dissolved hemoglobin or hemocyanin• Explosive cells release a clotting agent at injury sites
Heart Shape
• Heart long and tubular; to postcephalic region• Or, globular, box shape, in thorax; association
with thoracic gills
Gas Exchange
• Aquatic– Small organisms = diffusion– Concealed gills for protection, prevent dessication– External gills
• Modified thoracic limbs• Gills are thin; maximize gas exchange• Most species beat gills to maintain flow
Gas Exchange
• Terrestrial– Cutaneous Respiration
• Membranes on legs of some species
– Gills• Concealed
– Pseudotrachea• Internal blind sacs to outside through small pores• Air in sacs, gas exchange with blood • Internal gills moist
Feeding Strategies
•Water currents•Hydraulic vacuum•Filter feeding•Feeding basket•Passive•Twirling antennae•Direct manipulation•Sand grazers or Sand lickers•Predators•Parasitism
Water Currents• Thoracic limbs for swimming and creating
suspension feeding currents• Water drawn into space • Particles trapped by setae• moved to food groove and toward head
Hydraulic vacuum
• Mouth appendages = paddles
• Water containing food drawn into interlimb space
• Food particles are not filtered, but captured in small parcels of water
• Individual algal cells are captured this way
Filter feeding
• Sessile crustaceans have feathery cirri to filter feed
• food up to one mm• = detritus, bacteria, algae and various
zooplankton• Some can coil cirrus around large prey in a
tentacle fashion
Filter feeding in slow water
• Extend pairs of cirri like a fan• Sweep rhythmically through water
Filter feeding in fast water
• Allow water to run through filter• video
Passive feeding
• Use cirri to passively strain• Burrow into sand with anterior facing upward• Extend cirri to capture bacteria, protists and
phytoplankton• Antennae brush food towards mouth
Twirl antennae
• Create spiraling currents that bring food toward mouth
• Food entangled in setae near base of mouth, brushed in
Direct manipulation
• Manipulation by mouthparts, pereopods and subchelate anterior legs
Sand grazers or Sand lickers
• Brush sand grains with setose mouthparts
• Select individual sand grain, rotate and tumble against mouthparts to remove organic material
Predator
• Grab prey with chelae pereopods• Tear, grind and shear with mouthparts
• Hunters or ambushers use raptorial subchelae to stab, club or smash prey
• Some hold prey in cage using endopods; others inject and suck out tissues
Snapping Shrimp
• Use large cheliped to snap close: produces loud popping sound and “shock” wave
• Pressure wave stuns prey, pull into burrow
• Foregut– Lined with cuticle that is continuous with exoskeleton, molted– Short pharynx-esophagus, stomach– Stomach = chambers for storage, grinding and sorting
Digestive system
HindgutHindgut Short, to anusShort, to anus
Midgut intestine Length varies with
shape size, diet
digestive ceca
Excretion and Osmoregulation
• Ammonia by nephridia and gills• nephridial excretory organs as antennal glands
(green glands) or maxillary glands
• Inner blind end is coelomic remnant of nephridium = sacculus
• Sacculus - Actively remove and secrete material from blood into excretory lumen
• metabolic waste removal and water and ion balance
Other osmoregulation
• Thin areas of cuticle– Gill surfaces
• terrestrial isopods: ammonia diffuses from the body as gas
Nervous System and Sense Organs
• CNS• Brain: three fused ganglia• Protocerebrum• Deutocerebrum• Tritocerebrum• Primitive nervous system = ladderlike
Nervous System and Sense Organs
• variety of sensory receptors• innervated setae or sensilla: contain
mechanoreceptors and chemoreceptors
• Propioceptors
• Animals in Class Malacostraca: statocysts
Nervous System and Sense Organs
• Two rhabdomeric photoreceptors:• Median simple eyes• Lateral compound eyes• Most possess both, either simultaneously or
during development
• Naupliar eye = primitive, secondarily lost
Nervous System and Sense Organs
• Lateral compound eyes• Lack visual acuity• Discern shapes, patterns and movement• Color vision in some• Lacking in many taxa
Nervous System and Sense Organs
• Underwater vision• Problems with angular distribution of light, lower intensity,
and narrow range of wavelengths than in air
• Solution: Mount eyes on stalks, increase information available to eyes. Increases field of view, and binocular range
Nervous System and Sense Organs
• Complex Endocrine and Neurosecretory Systems• Not well known
• Molting, chromatophore activity, and reproduction under hormonal and neurosecretory control
• Bioluminescence in several groups
Reproduction And Development
• Exploit virtually every life history scheme imaginable
• Usually dioecious• Hermaphroditism in remipedes,
cephalocarids, cirripedes, few decapods• Parthenogenesis common among
branchiopods and certain ostracods
Reproduction And Development
• Gonads paired structures in trunk• Pair of gonoducts from gonads to genital
pores on trunk segment• Male pair of penes, or single fused median
penis• Female include seminal receptacles• Most Crustacea Copulate in Pairs