Phylum Echinodermata

Classification

• Class Crinoidea - sea lilies and feather stars. Aboral attachment of stalk of dermal ossicles. Anus on oral surface; five branching arms with pinnules; ciliated ambulacral groove on oral surface with tentacle-like tube feet for capture of food; spines and pedicellariae absent. Examples: Antedon and Florometra spp.. Found in all seas except the Baltic and Black seas. Most are subtidal, although some are found in very deep waters of 5000 meters. The free-living feather stars prefer rocky bottoms and are most abundant in shallow tropical lagoons. The sea lilies are stalked and sessile, preferring muddy sea bottoms and deep waters.

• Class Asteroidea - sea stars. Star shaped, with arms not sharply marked off from central disc; ambulacral grooves open, with tube feet on oral side; tube feet often with suckers; anus aboral; pedicellariae present. Example: Asterias sp.. Found along rocky, coastal bottoms, often in tidewater regions; also, may be found in deep waters far from shoreline.

• Class Ophiuroidea - brittle stars. Star shaped, with arms sharply marked off from the central disc; ambulacral grooves closed, covered by ossicles; tube feet without suckers and not used for locomotion; pedicellariae absent. Example: Ophiura sp.. Found in all oceans and at nearly all depths. Many are shallow-water, sedentary forms.

• Class Echinoidea - sea urchins, sea biscuits, and sand dollars. More or less globular or disc shaped, with no arms (rays); compact skeleton or test (calcium carbonate shell), with closely fitting plates; movable spines; ambulacral grooves closed and covered by ossicles; tube feet with suckers; pedicellariae present. Are mostly benthic along rocky coastlines and in tide pools; sometimes found in sandy regions and coral reefs.

• Class Holothuroidea - sea cucumbers. Cucumber shaped; with no rays or spines; microscopic ossicles embedded in thick muscular wall; anus present; ambulacral grooves closed; tube feet with suckers; modified tube feet form small tentacles; pedicellariae absent. Are benthic and generally sluggish animals common in intertidal muddy or sandy bottoms, usually where decaying marine vegetation accumulates (are considered decomposers).