Cnemodesmus riparius Shelley & Crawford, 1996

Vohland, Katrin & Hamer, Michelle, 2013, A review of the millipedes (Diplopoda) of Namibia, with identification keys and descriptions of two new genera and five new species, African Invertebrates 54 (1), pp. 251-251 : 258-259

Cnemodesmus riparius Shelley & Crawford, 1996

Figs 2–7

Cnemodesmus riparius: Shelley & Crawford 1996: 2–4 , figs 1, 2; Hamer 1998: 25.

Diagnosis: Gonopod solenomere slender, long, coiled with laminate, folded process along inner margin near midlength, femoral process club-like. Tibiotarsus with broad, short basal process and acute, more distal process ( Fig. 2).

The closest relatives of this species are C. thysanopus ( Cook & Collins, 1893) and C. calundensis Kraus, 1958 , from Angola. In C. thysanopus , the tibiotarsus is much longer and bifurcate, and the basal process more acute, while C. calundensis can be distinguished mainly by the less curved solenomere.

Description:

Size: Width 1.1–1.4 mm.

Colour: Dark brown, suture dirty white posterior to metatergites, dark spot medially giving animal appearance of having dorsal longitudinal band.

Head: Frons setose. Antenna becoming thicker distally, microsensilla on distal part of antennomeres 5+6 ( Fig. 7, ms).

Collum: Broadly rounded ( Fig. 3).

Tergites and sternites: Metatergal sulcus smooth and long ( Fig. 4). Paraterga narrow, projecting slightly backwards up to segment 19, distally rounded. Pleurotergal ridges thin, reaching to the mid-body. Surface smooth. Progonopodial sternite setose, postgonopodial sternite smooth. Sternite 5 with cones fused together, forming a subrectangular process ( Fig. 6).

Legs: Femur of legs on segments 4–6 with digitiform process ( Fig. 5, fp). Tibia of legs without brushes.

Gonopods: As in diagnosis.

Material examined: NAMIBIA: 1♂ Khomas district, Windhoek [22°34'12"S 17°05'01"E], 19.iv.1972, P.G. Olivier, under stone [anterior part crushed] ( SMN 21695 ) ( NMNW) .

Distribution: Namibia, Kuiseb [23°12'S 15°37'E] and Gaub [23°25'S 16°01'E] rivers, as well as Windhoek.

Habitat: In Namibia, the species is distributed along the ephemeral beds of the Kuiseb and Gaub Rivers. Specimens were located in wet silt along river banks and a distribution throughout the river system therefore seems probable. Windhoek, where the examined specimen was collected, is part of the Swakop River catchment area [22°16'S 15°45'E], but only a few kilometres southwest of Windhoek, the Kuiseb River catchment area begins ( Jacobson et al. 1995). The animals can only survive in this dry environment by selecting more humid places like deep silt deposits close to the river banks, from where they are presumed to emerge and aggregate on patches of green cyanobacteria under favourable conditions ( Shelley & Crawford 1996). Experiments concerning desiccation resistance showed great variability between individuals.

Remarks: The specimen examined is smaller than the measurements given for the holotype, which is in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA ( Shelley & Crawford 1996). Moreover, the solenomere is shorter, with the tips of the tibiotarsus more acute in the specimen examined. These differences are small enough to be regarded as falling within the range of variation of a species.