Amsterdam Expeditions to the West Indian Islands, Report 38. The distribution and zoogeography of freshwater Ostracoda (Crustacea) in the West Indies, with emphasis on species inhabiting wells

The distribution of freshwater Ostracoda in the islands of the West Indies and part of the Venezuelan mainland is discussed. The ostracod fauna of wells and epigean habitats is compared. Some species, e.g. Cypretta spp. are found significantly more often in wells, others are only found in epigean habitats, e.g. Hemicypris spp. and Cypris subglobosa. Some species are found significantly more often in epigean habitats, e.g. Stenocypris major, others seem to have no preference, e.g. Physocypria affinis and Cypridopsis spp. Joint occurrence of Ostracoda and other faunal groups in wells is studied, especially for hadziid amphipods, which are supposed to predate on small crustaceans. There may be some influence of the presence of hadziid amphipods on the distribution of some species of Ostracoda, but this could not be tested statistically for most islands and species. Some biogeographical models are discussed. Most ostracods seem to have arrived at the islands by dispersal. No ostracods were found representing evidence for the regression model of distribution and speciation. Practically all species seem to be genetically stable and did not evolve into true hypogean species. Only in the presumably older islands Hispaniola and Cuba, true hypogean species are found, which seem to have evolved from relict freshwater ancestors. The results strengthen the hypothesis that Cuba and Hispaniola have been part of a proto-Antillean arc, which has been connected with Yucatan. The fact that no hypogean species were found in the Lesser Antilles strengthens the hypothesis that these islands have emerged above the sea level independently of the Proto-Antilles and much later in time.