Echinus

(e-kī´nus), Sea-urchin , or Sea-egg , a genus of marine animals, the type of an order (Ech i no idea) of the phylum Echinoderm at a (see above). In this type the body is spheroidal and invested in a test or shell composed of regularly arranged plates closely united together. It is covered with movable spines articulated by ball-and-socket joints. The mouth is situated in the centre of the under surface, and there is a complicated masticatory apparatus (Aristotle's lantern) consisting of five chisel-ended teeth 150 supported by an elaborate framework. The anus is similarly placed on the upper side, and is surrounded by a circlet of ten plates (apical disc), one of which bears a furrowed tubercle (madreporite) perforated by small holes through which water enters the water-vascular system. Locomotion is effected by meridional rows of tube-feet, aided by the spines. E. esculent us and some other species are edible. See Sea-urchin . IMG:3349192321007894546_v04image088.png:Echinus Echinus