These animals have an endoskeleton of calcareous ossicles and, hence, the name Echinodermata (Spiny bodied) . All are marine with organ-system level of organisation. The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical. They are triploblastic and coelomate animals. Digestive system is complete with mouth on the lower (ventral) side and anus on the upper (dorsal) side. The most distinctive feature of echinoderms is the presence of water vascular system which helps in locomotion, capture and transport of food and respiration. An excretory system is absent. Sexes are separate. Reproduction is sexual. Fertilisation is usually external. Development is indirect with free-swimming larva. 

Phylum Echinodermata can be divided into five classes.

Class 1 Crinoidea

Example:  Antedon (Sea lily)

Class 2 Ateroidea

Example: Starfish


Class 3 Ophiuroidea

Example: Ophiura (Brittle star).

Class 4 Echinoidea

Example : Sea urchins, Salmacis, Echinus

Class 5 Holothuroidea

Example:Cucumaria (Sea cucumber)

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