Terrestrial molluscs of Pemba Island, Zanzibar, Tanzania, and its status as an "oceanic" island

  • Rowson B
  • Warren B
  • Ngereza C
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Abstract

Pemba is thought to have had a longer and/or stronger history of isolation than its better-known counterpart, Unguja. The extent to which the biota support this hypothesis of greater oceanicity have been debated. Here, Pemba's terrestrial mollusc ("land-snail") fauna is surveyed and reviewed for the first time. We find at best equivocal evidence for the following hallmarks of greater oceanicity: impoverishment, imbalance, and a high rate of endemism. At least 49 species are present, families are represented in typical proportions, and there are only between two and four island-endemic species - i.e. a 4% to 8% rate of endemism. For land-snails, isolation thus seems to have been short (Pleistocene) or, if longer, weak. Nevertheless, Pemba does host endemic and globally rare species. Forty-five percent of the species found, including most of these, is restricted to forest reserves, with Ngezi Forest Reserve particularly rich. A further 45% are able to tolerate the island's woody cultivated habitats. One new snail species (Cyclophoridae: Cyathopoma) and one new slug species (Urocyclidae: Dendrolimax pro tem.) are described. New data and illustrations are provided for other taxa.

Author-supplied keywords

  • Caenogastropoda
  • Cyathopoma
  • Dendrolimax
  • Endemism
  • Land-snails
  • Mollusca
  • Pemba
  • Pulmonata
  • Slugs
  • Snails
  • Stylommatophora

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Authors

  • B. Rowson

  • B. H. Warren

  • C. F. Ngereza

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