ABSTRACT
Echinoderm ata: the animal phylum containing sea urchins and starfish. Members of the Echinodermata share the following features:
• adult members of the phylum show a pentamerous radial symmetry. This is a five-way symmetry. A starfish, for example, has five arms so there are five ways in which it can be cut to produce pieces that are a mirror image of each other
• they have a unique water-filled vascular system. Sea water enters the animal and flows along a series of canals to the tube feet. These tube feet have a number of functions including gas exchange, excretion and locomotion
• they have a thin epidermis, immediately under which is a layer of spines and plates made of calcium carbonate.
