The Echinoid Directory

Many sand dollars have a system of shallow grooves radiating from the mouth. These are termed food grooves (fg) and, as the name implies, their primary function is in the transportation of food particles to the mouth. They usually branch as they pass outwards towards the periphery and become progressively finer. The food grooves thus form an extensive network over the oral surface of the test. In sand dollars with lunules the food grooves always pass close to lunule openings. The detailed pattern of branching provides an important systematic character.

Food grooves are lined with stubby tube-feet and transport food particles in one of two ways. First fine particles can be swept along in ciliary currents towards the mouth. Alternatively, fine particles can be caught by the sticky tube-feet and moved towards the mouth in mucous feeding strings that run along the floor of the grooves. The food grooves thus act as conveyor belts for moving fine organic particles that fall around the test periphery or are picked up from beneath by the tube-feet.

Dendraster, the only sand dollar known to suspension feed by elevating its test out of the sediment, is unusual in having food grooves extending onto the aboral surface, and can thus capture food particles from both test surfaces.