Phylum Echinodermata (Echinoderms)

General characteristics Invertebrates Marine environments not cephalized, no head Deuterostromes (blastopore forms an anus) Coelmates embryos have radial cleavage

4 major unique characteristics 1- radial symmetry – Often pentaradial symmetry, body parts extend from the center along five spokes 2- endoskeleton made of ossicles- calcium carbonate plates – may be attached to spine – Or spicules that protrude through skin, forms echinoderm- “spiny skin” 3- water-vascular system – Network of water-filled canals 4- Tube feet – Small, movable extensions of the water vascular system – Used for movement, feeding, respiration, and excretion

Evolution Fossil record dates back to more than 500 million years (the Cambrian period) Early echinoderms were sessile Only 80 species still sessile Now some can crawl slowly along ocean bottom The bilaterally symmetrical larvae resemble it’s ancestors Most closely related to chordates

Class Crinoidea means “lily-like” Five arms branch to form many more arms Mucus covered tube feet filter organisms from the water Cilia then transport the organisms to the mouth Sea lilies -Sessile adults Uses a long stalk to attach to rocks or the sea bottom Feather stars – Can swim and crawl as adults Most species are extinct Feather star – Florometra serratissima

Class Ophiuroidea Means “snake-tail” Long, narrow arms allow them to move quicker than other echinoderms – Tube feet not used for movement Basket stars have thin, flexible limbs form coils that look like tentacles Parts of brittle stars break off easily – Can regenerate green brittle star – Ophiarachna incrassata Basket star – Gorgonocephalus eucnemis

Class Echinoidea Means “spinelike” Sea urchins and sand dollars Test- rigid exoskeleton, encloses internal organs Sea urchins have an Aristotle's mantle-complex jaw like mechanism, aids in movement Spines can contain poison Purple Sea Urchin – Heliocidaris erythrogramma Sand Dollar – Echinarachnius exentricus

Class Holothuroidea Means “water polyp” Sea cucumbers Armless Live on sea bottom, use tube feet to burrow Ossicles are very small and not connected, which means their body is soft California sea cucumber - Parastichopus californicus

Class Asteroidea Starfish – Carnivorous (mollusks, worms, other slow moving animals) – Can slowly pull clam apart use a cardiac stomach to begin digestion withdraws the stomach finishes digestion Red-knobbed sea star- Protoreaster linckii

Sea Star digestion Mouth – Cardiac stomach- short esophagus – Pyloric stomach – Digestive glands (in each arm) secrete enzymes that break down food – Nutrients go to the coelem – Undigested material expelled through anus

Sea Star external structure The aboral surface (top half) is covered in short spines – rough texture Pedicellariae- tiny pincers that surround the short stems – keep the body free of foreign objects, ex. Algae or other small animals

Sea Star Body Systems --No circulatory system – No excretory system – No respiratory system Fluid in the coelem distributes nutrients and oxygen Diffusion through skin gills on tube feet (respiratory gases and waste) – Skin gills- hollow tubes, stretch from coelem to exterior

Nervous system No head= no brain Nerve ring instead (circles the mouth) Radial nerve runs from the nerve ring along each arm Together coordinate tube feet movement Nerve net near body surface controls movement of spines, pedicallariae, and skin gills Eyespot at the end of each arm responds to light Several tentacles and tube feet respond to touch Touch-sensitive and chemical-sensitive cells are scattered all over the surface of the sea stars body

Reproduction and development Most have separate sexes Each arm contains a pair of ovaries and testes External fertilization, Larvae develops bilaterally symmetrical, called bipinnaria Some retain their larvae in their body or among their tentacles Can regenerate arms, but it takes about a year – Can shed an arm to escape a predator If an arm is attached to a portion of the central region, a whole new organism can develop Some species reproduce asexually – By splitting it’s body through the central region

Sea Star Water-Vascular System Water enters through the sieve-like madreporite on the aboral surface Passes through stone canal Then the ring canal Then the Radial canals Contraction of muscles surrounding ampulla cause the tube feet to expand and contract Ends of tube feet act as suction cups Allows the sea star to move

Works Cited Charton, Barbara. "sea star." The Facts On File Dictionary of Marine Science, New Edition. New York: Facts On File, Inc., Science Online. Facts On File, Inc. DMSN1384&SingleRecord=True (accessed April 9, 2009). "Echinoderms: Features." Animal Anatomy On File, New Edition. Copyright Diagram Visual Information Ltd., Science Online. Facts On File, Inc. A0439&SingleRecord=True (accessed April 9, 2009). Edward J. Devillez, "Digestion (invertebrate)", in DOI / David L. Pawson, Andrew C. Campbell, David L. Pawson, David L. Pawson, Raymond C. Moore, J. John Sepkoski, Jr., "Echinodermata", in DOI /