Phylum Echinodermata - NEET-Biology

 Phylum Echinodermata

Fig: Sea urchin (Echinodermata)

Important characteristics:

• Exclusively marine & benthic i.e. found at the bottom of the sea.

• Spiny skinned free swimming, triploblastic & coelomate animals.

• Adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical.

• Lack of head and do not show segmentation.

• The digestive system is complete with the mouth on the ventral side & anus on the dorsal side.

• The most characteristic feature in Echinodermata is the presence of the water vascular (or ambulacral) system. Tube feet are contractile appendages of the water vascular system; serve for locomotion, food capture, respiration & attachment of the body to the substratum. They constitute glands & filtering devices.

• Respiratory organs are skin gills or papulae (starfish), peristomial gills (sea-urchins), genital bursae (brittle stars), cloacal respiratory tree (holothurians).

• Perform sexual reproduction. Sexes are separate. Fertilization is usually external. Development is indirect with free-swimming larva.

The phylum Echinodermata is divided into two subphyla:

• Pelmatozoa: It has a single living class Crinoidea represented by sea lilies or feather stars like Antedon, Rhizocrinus, etc.

• Eleutherozoa: It has four living classes: Asteroidea (Asterias), Ophiothrix, Echinoidea (sea urchin), Holothuroidea (sea cucumbers).

Fig: Sea cucumber (Holothuroidea)