The role of external appendages in the distribution and life habits of the sand dollar Echinarachnius parma (Echinodermata: Echinoidea)


  • *Dept. of Geology, Louisiana State University. Baton Rouge, Louisiana 70803, U.S.A.


The action of the aboral podia is one of the key factors controlling the wide distribution of the clypeasteroid Echinarachnius parma. According to field and laboratory studies (Gulf of Maine), E. parma gathers and selects food primarily from its aboral surface, which is naturally orientated just below the nutrient rich, uppermost sediment layer. Compared to Mellita, wider spacing between the aboral spines in E. parma permits silt and larger particles to be ingested and the action of podia allows it to burrow, and thus gather food, in a wider range of sediments. The broad ecologic tolerance of E. parma rather than specialization, facilitated the biological success of this species. The variation in arrangement of podia on the tests of clypeasteroids suggests interspecific differences in feeding and burrowing strategy.