A new genus for the freshwater crab Potamonemus asylos Cumberlidgeı 1993 ı (Brachyura: Potamoidea: Potamonautidae) from Cameroonı Central Africaı with a key to the genera of the Potamonautinae Author Cumberlidge, Neil Author Mvogo Ndongo, Pierre A. Author Clark, Paul F. Author Daniels, Savel R. text Journal of Natural History 2019 2019-05-10 53 11 659 676 journal article 10.1080/00222933.2019.1583390 d67f767a-7d54-4fd9-9032-619d863b9ae8 1464-5262 3675494 Potamonemus Cumberlidge and Clark, 1992 ( Figures 2 (a,b), 3(a,b), 4(b,c), 5(c – f), (h,i), 6(c – f), 7(b,c,e,f) and 8(b,c,e,f,h,i)) Potamonemus Cumberlidge and Clark, 1992: 49 , figs 1 – 3, tables 1 – 2, pl. 1; Cumberlidge, 1999: 208 – 209, fig. 64D Rediagnosis Mandibular palp 2-segmented, lacking flap at junction between segments ( Figure 8 (h,i)); G1 TA slim, curving outward, long (TA/SS 0.63), lacking setae, tapering to pointed tip ( Figure 7 (b,c,e,f)); G2 TA distinctly shortened (TA/SS 0.13, Figure 8 (b,c)). Description See Cumberlidge and Clark (1992) and Cumberlidge (1999). The carapace proportions of all known specimens of P. mambilorum have been recalculated in the present study (CW/FW 3.08, CW/FW 2.22, and CW/FW 0.96), and the relative lengths of the TAs of G1 and G2 of P. mambilorum (TA/SS of 0.63 and 0.13 respectively) are presented here for the first time. Figure 3. Potamonemus sachsi Cumberlidge, 1993 , adult ♂, CW 31.6 mm, Obudu Plateau, Nigeria (NMU 8.IV.1983A). (a) Whole animal, dorsal view; (b) whole animal, ventral view. Scale bar: 6.3 mm. Photographs by Phillip Crabb, NHM, London. Scale bar: 19 mm. Type species Potamonemus mambilorum Cumberlidge and Clark, 1992 , by original designation. Type locality Somié, Cameroon . Species included Potamonemus mambilorum and P. sachsi Cumberlidge, 1993 . Figure 4. Frontal view of carapace. (a) Buea asylos ( Cumberlidge, 1993 ) comb. nov. , holotype, adult ♂ CW 27.6 mm, between Buea and Kumba, Cameroon (NHM 1994.587). (b) Potamonemus mambilorum Cumberlidge and Clark, 1992 , holotype, adult ♂, CW 34.5 mm, Somié, Cameroon (NHM 1991:183); (c) P. sachsi Cumberlidge, 1993 , adult ♂, CW 31.6 mm, Obudu Plateau, Nigeria (NMU 8. IV.1983A). Photographs by Phillip Crabb, NHM, London. Scale bar: a = 9 mm; b = 11 mm; c = 10 mm. Distribution Potamonemus is endemic to the rainforest zone of south-western Cameroon and southeastern Nigeria ( Cumberlidge 1993 , 1999). Remarks The carapace proportions of all known specimens of P. sachsi have been recalculated in the present study (see above), as have the relative lengths of the terminal articles of G1 and G2 of P. sachsi , and these characters can be used to distinguish the two species of Potamonemus from B. asylos comb. nov. Figure 5. (a–f) Frontal view of right and left chelipeds; (g–i) dorsal view of right cheliped carpus. Buea asylos ( Cumberlidge, 1993 ) comb. nov. , holotype, adult ♂ CW 27.6 mm, between Buea and Kumba, Cameroon (NHM 1994.587), length of right cheliped = 24.2 mm. (c–d) Potamonemus mambilorum Cumberlidge and Clark, 1992 , holotype, adult ♂, CW 34.5 mm, Somié, Cameroon (NHM 1991:183), length of right cheliped = 37.0 mm; (e–f) P. sachsi , adult ♂, CW 31.6 mm, Obudu Plateau, Nigeria (NMU 8.IV.1983A), length of right cheliped = 27.6 mm; (g) Buea asylos ( Cumberlidge, 1993 ) comb. nov. , holotype, adult ♂ CW 27.6 mm, between Buea and Kumba, Cameroon (NHM 1994.587); (h) P. mambilorum Cumberlidge and Clark, 1992 , holotype, adult ♂, CW 34.5 mm, Somié, Cameroon (NHM 1991:183); (i) P. sachsi Cumberlidge, 1993 , adult ♂, CW 31.6 mm, Obudu Plateau, Nigeria (NMU 8.IV.1983A). Figures (a–i) scaled for comparison. Photographs (a–f) by Phillip Crabb, NHM, London. Scale bar: a,b = 4.21 mm; c,d = 5.26 mm; e, f = 4.82 mm; g = 3.1 mm; h = 3.83 mm; i = 3.51 mm. Biogeography The freshwater crab fauna of Cameroon is dominated by species of Sudanonautes , and is most diverse in south-west Cameroon where there are two endemic genera ( Louisea and Buea gen. nov. ), two species of Potamonemus , and a single species of Potamonautes (N. Cumberlidge unpub. data). Biogeographically, the affinities of the freshwater crabs of Cameroon lie with those of its neighbouring countries ( Nigeria , Central African Republic , Congo , Gabon , and Equatorial Guinea /Bioko) which occupy a forested part of Africa to the north of the Congo River that is bounded by the north-west coastline of Central Africa. The freshwater crab fauna of this part of Africa is dominated by species of Sudanonautes and is remarkable for the almost complete absence of species Potamonautes (Cumberlidge 1999) , which is the most species-rich and most widely distributed genus in sub-Saharan Africa (N. Cumberlidge, unpub. data). The freshwater crab fauna of Cameroon is unusually diverse (15 species in five genera), especially given the relatively small size of this Central African country ( 475,440 km 2 ). This species richness may be attributed to the abundance of stable lowland and highland equatorial forests and the numerous year-round water courses that are sustained over historical time by the high rainfall totals recorded for this part of Africa (Cumberlidge 1999; Mvogo Ndongo et al. 2017a ; 2017b , 2017c , 2018 ) ( Table 1 ). The present study underlines the importance of Cameroon as a biodiversity hotspot because it has the highest number of freshwater crab genera in the whole of the African continent (Cumberlidge 1999; Daniels et al. 2015 ; Mvogo Ndongo et al. 2017a , 2017b , 2017c , 2018 ), and only Madagascar (with seven genera) is more diverse in the Afrotropical region as a whole ( Cumberlidge and Sternberg 2002 ; Cumberlidge et al. 2017 ). Figure 6. Cheliped merus. (a–b) Buea asylos ( Cumberlidge, 1993 ) comb. nov. , holotype, adult ♂ CW 27.6 mm, between Buea and Kumba, Cameroon (NHM 1994.587), ventral view of right and left cheliped merus, respectively; (c–d) Potamonemus mambilorum Cumberlidge and Clark, 1992 , holotype, adult ♂, CW 34.5 mm, Somié, Cameroon (NHM 1991:183): (c) ventral view of right cheliped merus; (d) dorsal view of right cheliped merus; (e–f) P. sachsi Cumberlidge, 1993 , adult ♂, CW 31.6 mm, Obudu Plateau, Nigeria (NMU 8.IV.1983A), ventral view of right and left cheliped merus respectively. Scale bar: a,b = 3.40 mm; c,d = 4.2 6mm; e,f = 3.90 mm. Figure 7. Right G1, ventral view (a–c) and dorsal view (d–f). (a,d) Buea asylos ( Cumberlidge, 1993 ) comb. nov. , holotype, adult ♂ CW 27.6 mm, between Buea and Kumba, Cameroon, total G1 length 5.9 mm (TA 2.7 mm, SS 3.2 mm) (NHM 1994.587); (b,e) Potamonemus mambilorum Cumberlidge and Clark, 1992 , holotype, adult ♂, CW 34.5 mm, Somié, Cameroon, total G1 length 9.7 mm (TA 3.6 mm, SS 6.1 mm) (NHM 1991:183); (c,f) P. sachsi Cumberlidge, 1993 , adult ♂, CW 31.6 mm, Obudu Plateau, Nigeria), total G1 length 9.0 mm (TA 3.4 mm, SS 5.6 mm) (NMU 8.IV.1983A). Scale bars: 2.0 mm. Amended key to the genera of the African Potamonautinae 1 The recognition of the new genus and the re-diagnosis of the reorganised Potamonemus make it necessary to provide an amended key to the genera of the African Potamonautinae . 1a Carapace frontal margin lined by small teeth or distinct granules; external angles of front marked by either sharp forward-pointing spine or small granule; triangular downward-pointing tooth beneath each external angle … ............ ........... Platythelphusa 1b Carapace frontal margin smooth, external angles of front smooth (lacking spine, granule, or downward-pointing tooth) ................................................................................ 2 2a Carapace outline subhexagonal; outer margin of cheliped carpus with 2 or 3 sharp teeth; carpi and propodi of p2 – p5 with marginal spines................................ Erimetopus 2b Carapace outline transversely oval; outer margin of carpus of cheliped smooth, lacking teeth; carpi and propodi of p2 – p5 smooth, lacking marginal spines .... 3 3a G1 TA curving inwards towards medial line................................................ Liberonautes 3b G1 TA either straight or curving outwards away from medial line......................... 4 Figure 8. Right G2 ventral view (a–c); left third maxilliped, frontal view (d–f); left mandible, frontal view (g–i). (a) Buea asylos ( Cumberlidge, 1993 ) comb. nov. , holotype, adult ♂ CW 27.6 mm, between Buea and Kumba, Cameroon, total G2 length 4.3 mm (TA 0.9 mm, SS 3.4 mm, NHM 1994.587); (b) Potamonemus mambilorum Cumberlidge and Clark, 1992 , holotype, adult ♂, CW 34.5 mm, Somié, Cameroon, total length G2 5.3 mm (TA 0.9 mm, SS 4.4 mm, NHM 1991:183); (c) P. sachsi Cumberlidge, 1993 , adult ♂, CW 31.6 mm, Obudu Plateau, Nigeria, total length G2 6.8 mm (TA 0.8 mm, SS 6.0 mm, NMU 8.IV.1983A), (d) Buea asylos ( Cumberlidge, 1993 ) comb. nov. , holotype, adult ♂ CW 27.6 mm, between Buea and Kumba, Cameroon (NHM 1994.587); (e) P. mambilorum , holotype, adult ♂, CW 34.5 mm, Somié, Cameroon (NHM 1991:183); (f) P. sachsi , adult ♂, CW 31.6 mm, Obudu Plateau, Nigeria (NMU 8.IV.1983A); (g) Buea asylos ( Cumberlidge, 1993 ) comb. nov. , holotype, adult ♂ CW 27.6 mm, between Buea and Kumba, Cameroon (NHM 1994.587); (h) Potamonemus mambilorum Cumberlidge and Clark, 1992 , holotype, adult ♂, CW 34.5 mm, Somié, Cameroon (NHM 1991:183); (i) P. sachsi Cumberlidge, 1993 , adult ♂, CW 31.6 mm, Obudu Plateau, Nigeria (NMU 8.IV.1983A). Figures (a–i) not shown actual size; the size of these structures has been adjusted for comparative purposes. Scale bar: a = 1.57 mm; b = 1.76 mm; c = 1.94 mm; d = 5.5 mm; e = 5.9 mm; f = 4.4 mm; g = 1.6 mm; h = 2.4 mm; i = 2.3 mm. 4a Third maxilliped exopod with long flagellum ................................................................... 5 4b Third maxilliped exopod lacking flagellum ........................................................................ 6 5a Intermediate tooth on anterolateral margin between exorbital and epibranchial teeth .......................................................................................................................... Sudanonautes 5b No intermediate tooth on anterolateral margin between exorbital and epibran- chial teeth................................................................................................................ Potamonautes 6a G1 TA long (TA/SS 0.63 – 0.86), curving outwards, ending in pointed tip; G2 TA much shorter (TA/SS 0.13 – 0.23) ............................................................................................. 7 6b G1 TA weakly S-shaped, tube-like, ending in rounded tip; G2 TA very long, flagellum- like (TA/SS 0.64).......................................................................................................................... Louisea 7a G1 TA long (TA/SS 0.86), broadened in mid-section, with long marginal setae......... ........................................................................................................................................... Buea gen. nov. 7b G1 TA short (TA/SS 0.63), slim along entire length, lacking long marginal setae..... ............................................................................................................................................. Potamonemus