biogeographical significance of a new

species from Pemba Island, Tanzania Abstract The damselfly, Platycnemis pembipes sp. nov., is described from Pemba Island (Ngezi Forest, Tanzania) and its affinitieswithGuineo-Congolian andMalagasy congeners are examined. For this purpose the identity anddistributionof Afrotropical Platycnemis is reviewed, especially the taxonomically confused continental species. The Pemba species is nearly identical to some species of the Malagasy radiation of Platycnemis, but distant from the Guineo-Congolian species that have tropical Asian affinities. It is argued that the species is a long-distance wind-borne arrival from Madagascar, which survived due to favourable climatic conditions on Pemba. Habitats on the mainland, only 50 km further, are or have been drier and therefore seem unsuitable. The new species, living proof of a remarkable colonisation event, is under immediate threat, confined to a single stream in an imperilled forest, over 1000 km from its nearest relatives. The holotype of the enigmatic P. mauriciana, not recorded on Mauritius after its description, cannot originate from the island as it pertains to the European P. latipes. Five species recalling the Asian genus Copera are known in the male sex from central and western Africa; all were confused to some degree with P. congolensis and a key is given. The lectotype of P. congolensis is designated and its identity is clarified. Platycnemis flavipes and P. xanthopus are junior synonyms of P. nyansana. Discovery of the P. rufipes female showed that P. escherichi, known only from the female holotype, is a junior synonym of it. The generic classification of Platycnemis and Copera is not resolved, but data and hypotheses that should aid future analysis are provided