Diagnostic Features of Phylum Echinodermata

1. Free living exclusively marine forms.

2. Adults are radially symmetrical while larvae are bilaterally symmetrical.

3. Body is represented by a central disc which distinguishable into oral and aboral surfaces

4. Disc may bear extensions called arms.

5. Body triploblastic, coelomate without segmentation, head and brain.

6. The surface of the body is covered by calcareous ossicles or plates, often bea­ring tubercles or spines called pedicellaria.

7. On the underside are five grooves called ambulacra, radiating from the mouth to the tip of the arms,

8. They possess endoskeleton in the form of calcareous plate called ossicles embedded in the dermis.

9. Endoskeleton mesodermal

10. A unique water vascular system is present. which performs many functions.

11. Digestive system is complete. Digestive canal is a coiled tube , anus placed on the aboral side.
12. Presence of tubular contractile tube feet or podia used as locomotory organ and/or feeding organ.

13.Tube feet are extended and retracted by variation in hydraulic pressure of the fluid in them and contraction of their muscles.

14. Haemal circulatory system poorly defined.

15. There are no definite respiratory and excretory systems

16. Nervous system has a central nerve ring with five radiating nerves.

17. Reproduction is sexual. gonochoric (Sexes are separate).

18. Gonads simple in nature. Fertilization external. Development is indirect.

19. Development deuterostomatous, with  bilateral­ly symmetrical,  free swimming larval forms

20. Show very high power of regeneration.

Classes- Asteroidea,      eg. Asterias; Ophiuroidea,    eg. Ophiothrix; Echinoidea,      eg. Echinus; Holothuroidea, eg. Sea cucumber, Crinoidea,        eg. Sea lily.