Endemism in the Cladocera (Crustacea: Branchiopoda) of Southern Africa

We review the current state of knowledge and patterns of distribution in the endemic Cladocera (Crustacea: Branchiopoda) of Southern Africa and describe two species of the Western Cape, of which one is new to science. Frey (1993), Korovchinsky (2006) and Smirnov (2008) previously suggested that South Africa harbours few endemics in the Cladocera. In the current study, we show that so-called low endemism in this region is mainly attributed to our limited state of knowledge of the local cladoceran fauna. Many of the South African taxa are ignored and revisions are lacking, as we briefly discuss for the genus Daphnia. We list known Southern African endemic Cladocera with notes on their status, map the distributions of well-studied taxa, and discuss the importance of temporary freshwater rockpools. We confirm that Southern Africa is a region of endemism for the group. We recognise three categories of endemics: i) Montane endemics in the East (e.g. Drakensberg mountains); ii) endemics of the Western Cape (lowlands); iii) South African endemics, widely distributed in the region, both in the mountains and the lowlands.

South African endemics have previously been regarded as relicts (Korovchinsky 2006), yet for the two taxa explored in detail in this study, there are no specific primitive morphological characters in comparison to congeners (within their respective genus/species group) and the morphology mainly suggests strong isolation. The two species belong to the Chydoridae and the Eurycercidae, respectively, and are used here as case studies for the investigation of Western Cape endemics.

The first, Alona capensis Rühe, 1914 (Anomopoda: Chydoridae: Aloninae), is redescribed based on the type material. We discuss the affinities of this enigmatic species for the first time. Morphology of the habitus and the postabdomen parallel that of members of the Alona affinis-complex. The disconnected head pores and limb characters, on the other hand, place A. capensis in the Alona pulchella-group, a different lineage in the Aloninae subfamily. The specific postabdomen shape of A. capensis and a unique, inflated rostrum, diverge from the main A. pulchella-morphotype and illustrate the significant morphological isolation of A. capensis within its group.

The second species, Eurycercus (Eurycercus) freyi sp.nov. (Eurycercidae), is described based on material from the collection of the late Prof. Dr. David G. Frey. It is an E. lamellatus-like taxon that is easily differentiated from the two related species (E. lamellatus and E. microdontus) by a strong indentation (with depth larger than head pore diameter) behind the head pores. E. freyi sp.nov. seems to be the closest relative of E. lamellatus. The small clade of just two species is supported by two synapomorphies: i) the rostrum is long; and ii) the spine situated on the proximal segment of the exopod of antenna II is longer than the second segment, in contrast to E. microdontus.