Echinoidea - Sea Urchins and Sand Dollars
Spherical to disc-shaped ECHINODERMATA whose skeletal plates, usually joined to form a rigid test, bear independent movable spines and other external appendages. Five radial areas (ambulacra) with plates perforated for passage of tube feet. Locomotion is slow, effected by tube feet or movement of spines. The regular urchins are usually dark in colour, whereas the irregular urchins are coffee-brown to off-white. "Regular" urchins have obvious radial symmetry, a central mouth on the underside and a central anus on the upper surface. In "irregular" forms, there is a more or less pronounced bilateral symmetry, with mouth central or anteriorly positioned, and with anus posterior.
Of more than 800 known species, 15 have been recorded from Bermuda.
On hard and soft bottoms to several hundred meters in
depth. Regular urchins mostly on hard bottoms, or on surface of sand, irregular
urchins usually buried in sand. Some species (Lytechinus)
may occur locally in very large numbers.