Classification of Phylum Echinodermata

Phylum :- Echinodermata

Characters :- 

(i) Adult with radial & five rayed symmetry, while the larvae are bilaterally symmetrical.

(ii) The body is covered by calcareous ossicles or plates, often bearing projecting tubercles or spines.

SubPhylum :- Crinozoa

Characters :-

(i) Madriporite absent.

(ii) Radially symmetrical, possessing a cup shaped theca.

Class :- Crinoidea

Characters :-

(i) Arms are branched & bearing pinnules.

(ii) The ambulacral grooves radiates from the mouth & extend to the tip of the pinnules.

Examples :- Antedon (sea lily); Metacrinus;

Fig :- Antedon

Fig :- Metacrinus

SubPhylum :- Asterozoa

Characters :-

(i) Body is star shaped & remain unattached.

(ii) On the oral surface in the ambulacral groove, tube feet are present.

Class :- Asteroidea

Characters :-

(i) Arms are not sharply set off from the cetral dosc.

(ii) Anus & madriporite are present on the aboral surface.

Examples :- Asterias ; Asteropectin;

Fig :- Asterias

Class :- Ophiuroidea

Characters :-

(i) Arm sharply set off from the central disc.

(ii) Absence of ambulacral groove & arms are filled by vertebral ossicles.

Example :- Ophiura

Fig :- Ophiura

SubPhylum :- Echinozoa

Characters :-

(i) Radially symmetrical, globoid or discoid without arms or brachioles.

(ii) Madriporite & anus remain on the aboral surface.

Class :- Echinoidea

Characters :-

(i) Body more or less spherical, flattened orally/ aborally.

(ii) Aristotle's lantern, a apparatus used in feeding is mostly present.

Examples :- Echinus ; Arbacia;

Fig :- Echinus

Fig :- Arbacia

Class :- Holothuroidea

Characters :-

(i) Body elongated along oral/ aboral axis.

(ii) The surface of body may exhibit five ambulacral groove.

Examples :- Holothuria; Cucumaria;

Fig :- Holothuri

Fig :- Cucumaria