The patella (kneecap).

A mechanical device showing the motion of the sun and moon and their position for each day of the year. More fully "astronomical rotula".

A keyhole urchin or sand dollar of the West African genus Rotula (order Clypeasteroida), having a round, flattened test with deep notches along the edge. Also (in form Rotula): the genus itself.

Each of five radial elements forming part of the oral apparatus (Aristotle's lantern) of echinoids.

A circular structure forming the end of some sponge spicules; = "rotule". Also: a wheel-shaped spicule in the integument of certain holothurians.