Phylum Echinodermata (Gr., echinos = spiny + derma = skin, ata = characterised by) includes exclusively marine invertebrates displaying pentamerous radial symmetry and an endoskeleton of calcareous plates and spines. Jacob Klein gave the name echinodermata. This phylum is a collection of about 7,000 living species and constitute some of the most beautiful members of sea fauna, such as starfishes or sea stars, sea urchins, sea cucumber, sea Tillies and sand dollars etc. The name 'starfish' is, however, misleading as these animals are not true fishes. A more suitable name suggested for them is ‘sea star’,
The echinoderms are important both biologically and geologically. Biologically, there are few other groupings so abundant in the biotic desert of the deep sea, as well as shallower oceans. Echinoderms generally have remarkable powers of regeneration of tissue, organs, limbs, and of asexual reproduction, and in some cases, complete regeneration from a single limb. Geologically, the value of echinoderms is in their ossified skeletons, which are major contributors to many limestone formations, and can provide valuable clues as to the geological environment.
Echinoderms possess a simple digestive system which varies according to diet. In many species, the large cardiac stomach can be everted and digest food outside the body. Gonads are present in each arm. In echinoderms such as sea stars, every arm bears two rows of tube feet on the oral side which help in attachment to the substratum. Echinoderms are efficient scavengers of decaying matter on the seafloor. They prey upon a variety of small organisms, thereby helping to regulate their numbers. In addition, echinoderms produce vast numbers of larvae that provide food for other planktonic organisms.
Examples: Asterias (Star fish) Echinus (Sea urchin), Antedon (Sea lily), Cucumaria (Sea cucumber) and Ophiura (Brittle star).
