Anatomy Sand dollar

leodia sexiesperforata louis agassiz (1841)



examples of rotulidae




encope emarginata (aboral , oral faces) ernst haeckel (1904)



clypeaster rosaceus, ibid

sand dollars, members of order clypeasteroida, possess rigid skeleton known test. test consists of calcium carbonate plates arranged in fivefold radial pattern. in living individuals, test covered skin of velvet-textured spines covered small hairs (cilia). coordinated movements of spines enable sand dollars move across seabed. velvety spines of live sand dollars appear in variety of colors—green, blue, violet, or purple—depending on species. individuals dead or dying (moribund) found on beaches of external morphology still intact. dead individuals commonly found empty test devoid of surface material , bleached white sunlight.

the bodies of adult sand dollars, of other echinoids, display radial symmetry. petal-like pattern in sand dollars consists of 5 paired rows of pores. pores perforations in endoskeleton through podia gas exchange project body. mouth of sand dollar located on bottom of body @ center of petal-like pattern. unlike other urchins, bodies of sand dollars display secondary front-to-back bilateral symmetry. anus of sand dollars located @ rather @ top in urchins, many more bilateral features appearing in species. these result adaptation of sand dollars, in course of evolution, creatures lived lives on top of seabed (epibenthos) creatures burrow beneath (endobenthos).

the common sand dollar, echinarachnius parma, widespread intertidal zones considerable depths in ocean waters of northern hemisphere. can found in temperate , tropical zones. keyhole sand dollar (three species, genus mellita) found on wide range of coasts in , around caribbean sea.