The flower or star shaped form on the back (or top) of a sand dollar is formed by the paired holes of specialized tube feet that help with this kind of sea urchins' respiration. read more
The flower or star shaped form on the back (or top) of a sand dollar is formed by the paired holes of specialized tube feet that help with this kind of sea urchins’ respiration. read more
Unlike other urchins, the bodies of sand dollars also display secondary front-to-back bilateral symmetry. The anus of sand dollars is located at the back rather than at the top as in most urchins, with many more bilateral features appearing in some species. read more