Types specimens of echpnodermata
Before we begin the study of the selected specimens of the following echinoderms - Feather star, Brittle star, Sea urchin, Sea cucumber and Star fish. You should be aware that though members of the various classes of ecchinoderms often appear to be superficially different, however their structure is fundamentally similar. For example sea cucumbers tack the five arms of sea stars, but they do have five bands of tube feet and thus show the same basic pentaradiate symmetry.
Antedon is commonly called "feather star" or "sea lily" Examine the specimen and note the following features:
(i)The body of Antendon is made of a central convex disc of calyx and five equidistant, elongated slender radiating arms.
(ii)Each arm is divided into two branches at the base, so there are in effect ten long arms.
(iii)The arms are slender, flexible, movable and bear small spine-like structures or pinnules on the two sides.
(iv)The body has a distinct upper oral and lower aboral surface.
(v)Aboral surface bears several root-like, slender, curved, jointed cirri supported by small ossicles which help to attach Antedon to rocks.
(vi)Oral surface is covered with a soft and leathery skin, called tegmen and this surface bears the mouth and anus on the same side of the calyx. The anus is borne on a tiny papilla and is excentric whereas the mouth is in the center.
(vii)Five ambulacral ciliated grooves radiate from the mouth towards the arms. Each groove divides into two and runs along the oral surface of each arm.
(viii)The intervening body surface is the adambulacra.
(ix)Tube feet or podia are without suckers and can be seen along the edges of ambulacral groove.
(x)The exoskeleton is made of calcareous ossicles or plates.