ABSTRACT
Presence of shared synapomorphies in the respiratory structures of freshwater crabs strongly suggests a monophyletic origin for all groups. In the Trichodactylidae and other relatives from Africa plesiomorphy is more apparent, while in Pseudothelphusidae and other subgroups from West Africa and India, adaptation to air breathing has progressed further. The present distribution of both groups suggests a primitive Gondwanian distribution made disjunct by a mid-Cretaceous vicariant event. The most primitive Pseudothelphusidae categorized as such by the morphology of the third maxilliped, has a disjunct distribution the Greater Antilles and the Northern Andes of Colombia, explainable by a Pliocene vicariant event that isolated the Greater Antillean biota from that of Central and South America. The somatic and gonopodal characters form three distinct chorological series that radiate from northern Colombia to Central America and Mexico, to northern South America and the Guianas, and to the Southern Andes. Sympatries and the presence of geographic morphoclines indicate that this radiation of characters occurred in a series of dispersion events from a dispersion center in northern Colombia. The disjunct distribution observed in the Lesser Antilles and Guianas can only be attributable to chance dispersal after the Miocene. Consequently the present distribution of freshwater crabs in the neotropics cannot be understood simply in terms of either vicariance or dispersal, but as the result of a complex series of events.
