- 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).