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.Â
Phylum Echinodermata can be divided into five classes.
Class 1 Crinoidea
Example:Â 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)