BIOL 331, Lecture 10, Invertebrates II

BIOL 331
Lecture 10
Invertebrates II

Phylum Arthropoda (jointed foot)

General Characteristics

Exoskeleton of chitin

Segmented, bilaterally symmetrical

Jointed appendages

Growth requires molting

Classification

Subphylum Crustacea

Class Copepoda (copepods)

Class Cirripedia (barnacles)

Class Malacostraca (isopods, shrimp, crabs, etc.)

Subphylum Chelicerata

Class Merostomata (horseshoe crabs)

Class Pycnogonida (sea-spiders)

Subphylum Uniramia

Class Insecta (insects)

Subphylum Crustacea

General Characteristics

Gills
Skeleton hardened by CaCO₃
Appendages specialized (swimming, grasping, etc.)
Antennae with sensory functions
Stomach with chitinous teeth for grinding, bristles for sifting
Digestion extracellular
Open circulatory system
Ladder-like nervous system (except decapods)
Complex behavior
Compound eyes
Statocysts in some
Fertilization internal, mating often just after female molts, eggs often carried in special appendage
Females can store sperm for long periods
Larvae planktonic & varied
~35,000 species

Class Copepoda

Extremely abundant
Mouth parts filter food
First pair of antennae usually used for swimming
Some minute & parasitic

Class Cirripedia (barnacles)

Attached & enclosed in CaCO₃ shell
Feed by extending feet
Larvae are planktonic
Some are parasitic & lack shells

Class Amphipoda (beach hoppers)

Body compressed side to side
Head and tail often curved downward
Many scavengers, some parasites

Class Isopoda

Flattened dorso-ventrally
Similar lifestyles to amphipods

Class Malacostraca (decapods)

Characteristics	Examples
5 pairs of walking legs First pair of legs often pincers Cephalothorax covered by carapace Abdomen behind, often used for swimming Appendages near mouth called maxillipeds 2-chambered stomach Centralized nervous system	Shrimp & lobsters Laterally compressed Mostly scavengers some swim, some burrow Hermit crabs Hide soft abdomen in shell + laterally compressed, coiled Scavengers Crabs Dorsoventrally compressed Abdomen V-shaped in males, U-shaped in females Most scavengers

Subphylum Chelicerata

Class Merostomata (horseshoe crabs)

Horseshoe shaped carapace, 5 pairs of legs
Well represented in fossil record, 4 species now
Only found on East Coast

Class Pycnogonida (sea-spiders)

4 or more pairs of legs
Feed on soft invertebrates

Phylum Echinodermata

General characteristics

Radially symmetrical, often pentamerous
Oral/aboral orientation
Complete digestive tract in a coelom
Endoskeleton
Water vascular system, exchanges often through the madreporite
Tube feet with ampullae often opposite
Nerve net, but not well understood
5-10 or more gonads release gametes to water through duct
Often spawning is coordinated to maximize fertilization
Most larvae live in the plankton, some develop as eggs attached to parent
~6,000 species

Class Asteroidea

Characteristics	Examples
Usually 5 arms Endoskeleton made from separate plates Tube feet protrude from ambulacral groove Pedicellariae on aboral surface Predatory Feed by extruding stomach Oxygen exchange by small branching extensions of body wall Can reproduce asexually & regenerate arms	Pisaster – feeds on bivalves & "carrion" Henricia – blood star Sun star, numerous arms, feeds on other stars

Class Ophiuroidea

Arms and disk differentiated, arms jointed
Tube feet without suckers, move food to mouth
Mostly detritus feeders
~2,00 species

Class Echinoidea

Characteristics	Examples
Rigid test with movable spines Tube feet with suckers in five rows Mouth called Aristotle’s Lantern Most feed on algae Some are deposit feeders Oxygen exchange as for Asteroids ~900 species	Strongylocentrotus Heart urchins Sand dollars

Class Holothuroidea

No spines, not obviously radially symmetrical

Endoskeleton of microscopic calcareous spicules

5 rows of tube feet in most

Many are deposit feeders, tube feet around mouth help get food

Discharge fluid, sticky filaments, or viscera to deter predators

Breath through anus using respiratory trees

Phylum Hemichordata (includes acorn worms)

Characteristics

Intermediate between echinoderms and chordates
Some have larvae similar to echinoderms
Dorsal nerve cord
Gill slits along anterior part of gut

Acorn Worms

Deposit feeders, use mucous-secreting proboscis to move food to mouth
Live in U-shaped burrows
Some, over 2 m long, live near hydrothermal vents

Phylum Chordata

Characteristics

Dorsal nerve cord
Gill slits
Notochord
Invertebrate chordates often called protochordates

Subphylum Urochordata (tunicates)

Ascidians are the most common (class Ascidiacea)
Chordates because of tadpole larvae
Body is covered by a leathery tunic
Filter feeders with incurrent and excurrent siphons
May be solitary (Styela montereyensis) or colonial

Subphylum Cephalochordata

Separated from vertebrates only by lack of backbone
Laterally compressed & fish-like in appearance
Filter feeders, use gills

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