noun
: am ambulacrum in which the apical portion is expanded to form an area petaloid in outline on the aboral surface of the test (as in most irregular sea urchins)
noun
: am ambulacrum in which the apical portion is expanded to form an area petaloid in outline on the aboral surface of the test (as in most irregular sea urchins)
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012