Echinoderms

Phylum Echinodermata Echinodermata means “spiny skin” Echinoderms range in habitat from shallow coastal waters to deep ocean trenches Vary in size from 1 cm to 1 meter Organisms in this class include: Sea stars Sea Urchins Sand dollars Sea cucumbers

Characteristics Fossil record dates back 500 million years Ancestors were sessile, most species later evolved ability to move Deuterostomes blastopore develops into anus, mouth is secondary Makes them more closely related to Chordates

Characteristics Radial Symmetry Similar to cnidarians, have no sign of cephalization However, they develop from bilaterally symmetrical free swimming larvae (probably a sign of ancestry) Most have pentaradial symmetry Body parts extend from center along five spokes Three other major unique characteristics Endoskeleton made up of calcium carbonate plates called ossicles Water-vascular system Tube feet

copyright cmassengale Taxonomists have divided 7,000 species of echinoderms into five classes: copyright cmassengale

copyright cmassengale Crinoidea Asteroidea Ophiuroidea Echinoidea Holothuroidea copyright cmassengale

Crinoidea (“lily-like”) Include: Sea Lilies: Most closely resemble fossils sessile as adults Have long stalks that attach to rocks or the ocean floor Feather stars: can swim or crawl, but may stay in place for long periods Five arms extend from body and then branch Sticky tube feet that are at the end of each arm filter food and serve as a respiratory surface Mouth faces up

Crinoidea

Ophiuroidea (“snake-tail”) Largest echinoderm class (2,000 species) Basket stars: thin, flexible arms. Branch to form coils that look like tentacles Brittle stars: thin arms that break of easily and regenerate Primarily reside under stones & in crevices and holes of coral reefs Some feed by raking food off the ocean floor with their arms and tube feet Others trap suspended food with mucous strands between their spines.

Ophiuroidea

Echinoidea (“spine-like”) Test: rigid endoskeleton that the internal organs are compacted in Sea Urchins: Aristotle’s lantern: complex jaw-like mechanism that are used to grind their food Include teeth that surround the mouth protection: barbs on their long spines that are sometimes venomous Sand Dollars Found in sandy areas along sea coast Covered in short spines used for burrowing and locomotion

Echinoidea

Holothuroidea “water-polyp” Sea cucumbers Bodies are soft, armless Modified tube feet form fringe around mouth Feeding: tentacles around the mouth sweep up sediment from the water Protection: some can eject internal organs Lost parts are later regenerated Process called evisceration

Holothuroidea https://www.youtube.com/watch?v=wXf_YodWw40

Asteroidea (“star-like”) Starfish found all over coastal shores around the world prey on oysters, clams, and other sea food that is used by people

Structure & Function (Using the Starfish)

External Structure Typically have five arms, but some species have as many as 24 Oral surface: the underside of the body where the mouth is located Aboral surface: top of the body (opposite the mouth) Body is covered in short spines that give it rough texture Pedicellariae: tiny pinchers that surround each spine Protect and clean the body surface

Water-Vascular System Network of water filled canals connected to tube feet The path (figure 40-7) Water enters through madreporite (sieve-like plate on aboral surface Stone canal (tube pathway) Ring canal (tube that encircles mouth) Radial canal (tube that extends down each arm) Carry water to hundreds of hollow tube feet Valves prevent water from flowing backwards

Water-Vascular System Upper end of each tube foot expands to form a sac called the ampulla Muscles contract around the ampulla forcing water into tube feet and back out again This is how the starfish can extend or shorten the tube feet Enable locomotion

Feeding & Digestion Mouth – esophagus – cardiac stomach Cardiac stomach can be turned inside out through the mouth Transfers food to pyloric stomach Connects to a pair of digestive glands in each arm Most Sea Stars are carnivorous Mollusks, worms, slow moving animals

Other Body Systems No circulatory, excretory, or respiratory organ systems fluid in coelom bathes organs & distributes nutrients & oxygen skin gills: project through coelom lining; allow gas exchange and waste excretion nerve ring: surrounds mouth & branches off into nerve cords in each arm Radial nerve runs from ring down each arm If nerve is cut, tube feet lose coordination Eyespots: on end of each arm that responds to light Tentacles: responds to touch

Reproduction Most species have separate sexes each arm contains a pair of ovaries or testes Fertilization occurs externally Bipinnaria: free-swimming larva that a fertilized egg develops into After ~2 months settles in the bottom and develops into an adult through metamorphosis Regeneration: Process is very slow Use as a defense mechanism Can be used to reproduce asexually