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

By

Rowson, Ben
Warren, Ben H.
Ngereza, Christine

Type

Article

Date of Publication

2010

Original Publication

ZooKeys

Volume

70

Pages

1-39

Subjects

Land-snails, Stylommatophora, Pulmonata, Caenogast

Contributed by

Pensoft Publishers

Language

English

Published by

Sofia, Bulgaria Pensoft Publishers

Identifiers

DOI: https://doi.org/10.3897/zookeys.70.762

 

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.