- Any echinoderm of the order Clypeasteroida, having a flat, disk-shaped body with the mouth in a mid-ventral position, and living in sand, on or near the surface.
1987, John M. Lawrence, chapter I, in A Functional Biology of Echinoderms, page 75:
- In the sand dollars, the arrangement of the food grooves and consequently the lateral water vessels and their accessory tube feet is more complex (Phelan 1977).
2000, Sandra Alters, chapter I, in Biology: Understanding Life, page 692:
- Adult echinoderms have a five-part body plan corresponding to the arms of a sea star or the design on the "shell" of a sand dollar.
- 2001, Jennifer Hahn, Spirited Waters: Soloing South Through the Inside Passage, 2009, page 135,
- If you look carefully, a sand dollar is merely a sea urchin in flattened form.
- (any species of Clypeasteroida): clypeasteroid