What are the salient features of the echinoids ?

Explanation

1) It includes sea urchins, heart urchins, sand dollars etc. The body is ovoid or discoidal and covered by movable spines.
2) Arms are absent, tube feet are arranged in five bands and bear suckers.
3) Ossicles of the body unite to form a rigid tést or corona or case.
4) Pedicellaria are "three jawęd".
5) Anus and madreporite are aboral in position.
6) Ambulacral grooves are closed.
7) A complex five jawed masticatory apparatus called Aristotle.s lantern is present just inside the mouth. It is absent in heart urchins:
8) Life history includes larval form called echinopluteus,
9) Specialized gills called peristomial gills as present in sea urchins.