Strongylocentrotus purpuratus has a round body that consists of a radially symmetrical test, or shell, covered with large spines. The test itself ranges from 50mm in diameter to an occasional 100mm in diameter. This test is covered with spines that are generally bright purple for adults. Younger urchins have purple tinged spines that are mostly pale green in color. Also covering the test or shell, are tube feet and pedicellariae. The oral side of the urchin, on which the mouth is located, is usually the side facing the substrate (down). The aboral side of the urchin is usually the side of the urchin facing the observer (up). The body of S. purpuratus is radially semetrical. Male and female urchins are monomorphic; they are not physically distinguishable from one another. (Abbott et al., 1980; Olhausen and Russo, 1981; Ebert and Russell, 1988)