Contributions to Zoology, 77 (2) - 2008Neil Cumberlidge: Insular species of Afrotropical freshwater crabs (Crustacea: Decapoda: Brachyura: Potamonautidae and Potamidae) with special reference to Madagascar and the Seychelles
Continental islands

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Bioko (2,017 km2) (Equatorial Guinea) is located in the Gulf of Guinea about 40 km from Cameroon, 100 km from southern Nigeria and 160 km northwest of continental Equatorial Guinea. This volcanic island has forested mountains (3,308 m asl), a recent history of connection to the mainland, and supports two species of freshwater crabs, Sudanonautes floweri and S. granulatus, neither of which is endemic (Cumberlidge, 1993, 1995, 1999). Today both of these species are distributed over a wide area of West and Central Africa that includes the neighboring lowland coastal regions of Nigeria, Cameroon, Equatorial Guinea and Gabon (Cumberlidge 1999). These two species may have reached Bioko overland at a time when sea levels were lower and this island was united with the mainland.