Phylum Echinodermata includes marine invertebrates such as starfish, sea urchins, and sea cucumbers. They are characterized by radial symmetry, a water vascular system for movement and feeding, and an endoskeleton made of calcareous plates.
General Characteristics:
1) Habitat: The echinoderms are exclusively marine, non-colonial and largely bottom dwellers.
2) Body: They are triploblastic, coelomate animals.
3) Symmetry: The body exhibit radial and pentamerous symmetry in adult and bilateral symmetry in larval stage.
4) Body Surface: Body is distinguishable into oral and aboral surface without any differeniated head.
5) Ambulacra: The oral surface of the body is marked by five equidistant grooves called ambulacra, radiating from mouth to the tip of the arm with intervening grooves called interambulacra.
6) Digestion: Digestive system is complete.
7) Respiration & Excretion: There is no definite respiratory and excretory systems.
8) Locomotion Tube feet is present for locomotion.
9) Circulation: The blood vascular (Haemal) system is present in all echinoderms.
10) Nervous system: Nervous system is primitive and consists of a central nerve ring and 5 radiating nerves.
11) Pedicellariae: Surface of the body covered by calcareous ossicles with spines called pedicellariae.
12) Larva: Development of echinoderms involve a large number of ciliated and free swimming larval forms.
13) Reproduction: They are unisexual (larger species) or bisexual (small species). Fertilization is usually external.
Example: Asterias rubens (Star Fish); Ophiura sp. ; Clypeaster sp. ; Echinus sp. (Sea urchin); Cucumaria sp.(Sea cucumber); Antedon sp. etc