The systematic position of Unio caffer (Pelecypoda: Unionoida: Unionidae)

Abstract

Some anatomical, adult shell and larval features of Unto coffer Krauss are described and compared to those reported in previous accounts of this and other species. The findings necessitate the removal of U. caffer from the nominal genus Cafferia Simpson, for which it is the type species, and its return to the genus Unio Philipsson, in the Unionidae: Unioninae. Cafferia consequently becomes a junior subjective synonym of Unto.

Unio caffer is characterized in part by zigzag beak sculpture, dimorphic septal spacing between the marsupial, outer (comparatively dense) and the non-marsupial, inner (more distant) demibranchs and also within the marsupial demibranchs, the presence of perforated marsupial septa and imperforate non-marsupial septa, the occurrence of hermaphrodites in some but apparently not all populations, production of subtriangular glochidia with a hook at the ventral margin of each valve, short-term incubation of larvae in the marsupial demibranchs, and by its disjunct occurrence in the southern Ethiopian region (other Unio occurring only in the Palearctic).

These adult shell and anatomical features relate this species to those of several nominal genera in the Oriental region, although the latter are distinguished from it by the production of subovate, hookless glochidia.