Echinoids have basically three body plans: globular rounded tests, consisting of 20 rows of plates running from the anal region at the top to the lower mouth; sand dollars with flattened tests, a central mouth and the anus usually on the edge while the tube feet are usually restricted to a petal shaped region on the other side; and sea potatoes and heart urchins with rounded often elongated tests where the mouth is on the lower side and the anus is situated at the back, the tube feet are restricted to a small group around the mouth and a petal shaped region on the top. The regular shaped sea-urchins have a forest of large and small spines covering the test, while the sand dollars and heart urchins are covered by short spines in dense numbers giving them a furry look. The arrangement of spines and tube feet on plates is important, as is the overall shape of the test. In some cases it is necessary to examine the minute jawed grasping organs called pedicellariae which occur amongst the spines.
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