Echinoderms Diversity Echinodermata means spiny skin Echinoderms usually

Echinoderms

Diversity Ø Echinodermata means “spiny skin” Ø Echinoderms usually inhabit shallow coastal waters and ocean trenches Ø Organisms in this class include: • Sea stars • Brittle stars • Sand dollars • Sea cucumbers

Characteristics Ø Change from a free-swimming bilaterally symmetrical larva to a bottom-dwelling adult with radial symmetry. Ø Most have five radii or multiples which is known as pentaradial symmetry Ø They have an endoskeleton that is made up of calcium plates, may include protruding spines

Ø Have small feet called tube feet that aid in movement, feeding, respiration, & excretion. Ø Do not have circulatory, respiratory of excretory systems. Ø Have a nervous system but no head or brain. Ø There are two sexes and they can produce sexually and asexually.

Classes Ø Crinoidea Ø Asteroidea Ø Ophiuroidea Ø Echinoidea Ø Holothuroidea

Crinoidea (“lilylike”) Ø They include: Ø Sea lilies Ø Feather stars Ø Crinoidea are sessile: Ø they have long stalks that attach to rocks or to the ocean floor Ø feather stars eventually detach themselves Ø Sticky tube feet that are at the end of each arm catch food and serve as a respiratory surface.

Asteroidea (“star-like”) Ø Starfish or sea stars belong in this class Ø Found all over coastal shores around the world Ø Prey on oysters, clams, and other sea food that is used by people

Ophiuroidea (“snakelike”) Ø Largest echinoderm class Ø Includes basket stars & brittle stars Ø Primarily reside under stones & in crevices and holes of coral reefs Ø Have thin brittle arms that break off & regenerate themselves quickly Ø Feed by raking food off the ocean floor with their arms and bottom of tube feet

Echinoidea (“hedgehoglike”) Ø Sand dollars & sea urchins Ø Test: rigid endoskeleton that the internal organs are compacted in Ø Aristotle’s lantern: complex jaw-like mechanism that is used to grind their food Ø Locomotion: tube feet Ø Protection: barbs on their long spines that are sometimes venomous

Sand dollars Ø Live along seacoasts & sandy areas Ø Flat, round shape bodies; and adaptation for shallow burrowing Ø Locomotion: short spines (also aid in burrowing & cleaning their bodies) Ø Use tubes to filter food out of water

Holothuroidea Ø Sea cucumbers belong in this class Ø Bodies are soft Ø Feeding: tentacles around the mouth sweep up sediment from the water Ø Protection: eject internal organs through the anus. Ø Lost parts are later regenerated Ø Process called evisceration

Structure & Function copyright cmassengale

Body Plan of the Sea Star Ø Oral surface: mouth located on the underside of the body Ø Aboral surface: top of the body Ø Ossicles: sharp protective spines made of calcium plates, covered with thin epidermal layer Ø Pedicellariae: tiny forceps that protect and clean the body surface

Water-Vascular System Ø Hydrostatic pressure permits movement Ø Path of water in the Water-Vascular System u enters sieve plate (through madreporite) u Enters ring canal (encircles mouth) u. Enders 5 radial canals that extend to each arm

Ø Ampulla: bulblike sac that each foot connects to Ø Feet contract, water enters and are able to suction onto surface of slippery rocks

Feeding & Digestion Ø Use feet to attach Ø Eat mollusks, worms, and slow-moving animals Ø Pushes stomach out of body through mouth Ø Pours out enzymes Ø Enzymes help digest food Ø Pulls stomach and digested food back in

Other Body Parts Ø Fluid in coelom bathes organs & distributes nutrients & oxygen Ø Skin gills: protect coelom lining; gases are exchanged Ø Nerve ring: surrounds mouth & branches off into nerve cords in each arm. Ø Eyespots: on each arm that responds to light Ø Tentacles (arms): responds to touch

Reproduction Each arm produces sperm & egg Occurs externally Bipinnaria: free-swimming larva that a fertilized egg develops into Ø Settles in the bottom and develops into an adult through metamorphosis Ø Reproduce asexually by regenerating lost parts Ø Ø Ø