ABSTRACT
Juvenile sand dollar Dendraster excentricus selectively ingests iron oxide particles from the substrate. The selection is probably made by the buccal podia and at the floor of the buccal cavity and the selection is based on the density of sand particles or on the micro-flora on the sand surface, or both. Once ingested, the sand is stored in the intestinal diverticulum until the animal is two to three years old. There is some evidence that the sand may be dissolved in the diverticulum by organic acid or by iron-reducing bacteria. Structural and behavioural adaptations of the juvenile sand dollar are discussed.
