phylum echinodermata

• Subphylum Pelmatozoa– body in form of cup or calyx, borne on aboral stalk during part or all of life; madreporite absent; both mouth and anus on oral surface.
• Class Crinoidea– five arms branching at the base and bearing pinnules; ciliated ambulacral grooves on oral surface with tentacle-like tube feet for food gathering; madreporite absent. Ex. Sea lilies, feather stars
• Class Crinoidea– five arms branching at the base and bearing pinnules; ciliated ambulacral grooves on oral surface with tentacle-like tube feet for food gathering; madreporite absent. Ex. Sea lilies, feather stars
• Class Asteroidea – star-shaped with arms not sharply marked off from central disc; ambulacral grooves open with tube feet on oral side. Ex. Asterias (sea stars).
• Class Ophiuroidea– star-shaped with arms sharply marked off from central disc, ambulacral groove closed, covered by ossicles. Ex. Ophiura (brittle star)
• Class Echinoidea– more or less globular or disc-shaped with no arm, compact skeleton or known as test with closely fitting plates, movable spines; ambulacral groove closed; tube feet with suckers. Ex. Diadema (sea urchins), Heterocentrotus (pencil-slate urchin)
• Class Holothuroidea– cucumber-shaped with no arms, spines absent; microscopic ossicles embedded in thick muscular wall; ambulacral groove closed; tube feet with suckers. Ex. Holothuria (sea cucumbers).
• Subphylum Eleutherozoa – body star-shaped, globular, discoidal or cucumber shaped.