Biogeography of the marine Isopoda of the Indian Ocean, with a check-list of species and records

The marine isopod fauna of the Indian Ocean is reviewed in terms of its species diversity and biogeography. For the purposes of the review, the northeastern boundary of the Indian Ocean is defined at Cape Talpot in northern Western Australia and at Rottnest Island/ Perth in southern Western Australia. The history of isopod systematics in the Indian Ocean is reviewed by region, and the great lack of knowledge for Madagascar, parts of Western Australia, the east coast of Africa, and the continental shelf/slope overall, is noted. Previous research on the biogeographical provinces or regions of the Indian Ocean is briefly reviewed. For some groups of organisms, an impression of overall homogeneity for me tropical-subtropical area may prevail. However, close examination dispels the idea of homogeneity, and a number of sub-provinces or regions can be characterized. For a biogeographic review of the Indian Ocean marine isopods, a species list was compiled, which includes as many records for each species as could be found. This list contains approximately 1000 species in 303 genera. About 84% of the species are endemic to the Indian Ocean overall, but only 18% of the genera, a pattern consistent with the geological history especially of the Tethys Sea and the evolution of the Indian Ocean. This pattern is also consistent for a bendhic-dwelling group which lacks a pelagic stage and whose juveniles emerge from the brood-pouch as small versions of the adults. More than half the species are known from only a single record. Seven sub-provinces or regions are characterized in terms of their isopod fauna: 1. Sub-Antarctic Region, 79% of 135 species are endemic; 2. South African Region, 68% of 226 species are endemic; 3. Western Australia Region, 58% of 115 species are endemic; 4. East African Region, 46% of 144 species are endemic; 5. Red Sea Region, 63% of 105 species are endemic; 6. Indian Region, 62% of 268 species are endemic; and 7. Madagascar Region, 63% of 168 species are endemic. These levels of endemism are higher than those seen for most organisms for which data exist.