A contribution is made to the biology and behavior of two species of Dissodactylus. The six-lunuled sand dollar, Mellita sexiesperforata (Leske), is a newly discovered host for Dissodactylus crinitichelis Moreira in Barbados. The fourth species of clypeasteroid
with which this crab is known to associate, from 30% to 60% of the sand dollars examined housed crabs, which were normally located in the lunules or the food grooves. The frequency distribution of crabs on their hosts indicates a degree of aggregation which is probably attributable to sexually
mature pairs remaining together and to preferential settlement of megalopae on more shallow burrowing hosts. On exposed beaches the sand dollars burrow more deeply than on sheltered beaches and larger individuals burrow deeper than smaller ones. Depth of burrowing influences host selection
by the crabs but, apart from this, size of host (within the sample range) appears to be unimportant. Laboratory experiments indicate that D. crinitichelis leaves its host occasionally and may spend Some time away from it. Meoma ventricosa (Lamarck) is the first host to be
found for the previously little-known species, Dissodactylus primitivus Bouvier, and is the first non-clypeasteroid host for any species of Dissodactylus. From 80% to 100% of the M. ventricosa examined were found to house crabs, mostly externally, close to the mouth but
several were found inside the esophagus.
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