General characteristics of phylum Echinodermata:

(i) Their body is triploblastic, coelomate, unsegmented and radially symmetrical.

(ii) Digestive system is usually complete. Excretory organs are absent and anus is absent in class Ophiuroidea.

(iii) Body wall is covered with spiny hard calcareous plates that form a rigid or flexible endoskeleton.

(iv) Body cavity is organised into water vascular system, which moves respiratory and locomotary organs.

Examples: Antedon and sea urchin (Echinus)