Buea, Cumberlidge & Mvogo Ndongo & Clark & Daniels, 2019

Buea View in CoL gen. nov.

( Figures 1 View Figure 1 (a,b), 4(a), 5(a,b), 6(a,b), 7(a,d) and 8(a,d,g))

Potamonemus View in CoL – Cumberlidge 1993: 576 – 584, tables 2 – 3, figs 3 – 4, 5a – b, 6a – c (partim); Cumberlidge 1999: 15 – 16, 20, 24, 28, 50 – 51, 307, 309, 313, 355, 364, 374, 379 – 381, tables IX, X, XI, XII, XIII, fig. 40C, 41C, F, 42C, F, 43C, F, 44C, 53G, 61E, 65F (partim)

Comparative material examined Cameroon. Potamonemus mambilorum Cumberlidge and Clark, 1992 : Adamawa Region, holotype, adult ♂, CW 34.5, CL 25.5, CH 12.5, FW 11.5 mm, Somié, Bankim, Mayo-Banyo, Tikow Plain, 760 m asl, near border with Nigeria ( 6.50°N, 11.50°E), coll. D. Zeitlyn, 1991 (NHM reg. 1991: 183); several specimens, Elak-Oku, North-West region, coll. unknown, 20 October 2013. Potamonemus sachsi Cumberlidge, 1993 : Bamenda, holotype, adult ♂, CW 33.1, CL 22.6, CH 10.6, FW 10.6 mm ( ZIM K-30395). Paratypes, 3 ♂♂, CWs 32.8, 29.0, 26.0 mm, 4 ♀♀, CWs 34.4, 33.8, 33.4, 14.9 mm.

Nigeria. Cross River State, adult ♂, CW 32, CL 22, CH 10.5, FW 9.5 mm, south-east of Nigeria, Obudu Plateau, Oshie Ridge, Sankwala Mountain range, 1 km north of Obudu Cattle Ranch ( 6.383209°N, 9.386741°E), coll. N. Cumberlidge, 8 April 1983 ( NMU 8.IV.1983 A).

Diagnosis

Third maxilliped exopod either lacking, or with extremely reduced flagellum ( Figure 8 View Figure 8 (d)). Lower margin of cheliped merus with large pointed tooth distally ( Figure 5 View Figure 5 (a,b)). G1 TA long (TA/SS 0.86), directed outward, broad at base then narrowing sharply, distal one-third slender, tapering to pointed tip; lateral margin of G1 TA, SS with long bristles; longitudinal groove not visible when viewed from dorsal aspect ( Figure 7 View Figure 7 (a,d)); G1 SS basal margin very wide, 5× that of distal margin ( Figure 7 View Figure 7 (a,d)); G2 TA distinctly short (TA/SS 0.23) with pointed tip ( Figure 8 View Figure 8 (a)).

Distribution

Cameroon. Buea gen. nov. is endemic to the rainforest zone of south-western Cameroon ( Cumberlidge 1993, 1999).

Type species

Potamonemus asylos Cumberlidge, 1993 View in CoL by present designation and by monotypy.

Etymology

The genus is named for the town of Buea in south-western Cameroon which is close to the type locality. The name is used as a noun in apposition and the gender is masculine.

Species included

Buea asylos ( Cumberlidge, 1993) comb. nov.

Remarks

This new potamonautine genus is established to accommodate B. asylos comb. nov. which was previously considered to be a species of Potamonemus . Work by Daniels et al. (2015, fig. 2) prompted more detailed comparative studies involving the types of all three species currently assigned to Potamonemus . The morphological differences between the mandible and gonopod characters of B. asylos comb. nov. and the other two species of Potamonemus support the establishment of a new genus to accommodate P. asylos Cumberlidge, 1993 . The new genus is compared to the holotype of P. mambilorum from Cameroon (NHM reg. 1991: 183), the holotype of P. sachsi , from Bamenda, Cameroon (CW 33.1 mm, ZIM K-30395), and other specimens of P. sachsi (NMU 8.IV.1983 A) from Nigeria ( Cumberlidge 1993).

The main morphological differences that characterise Buea gen. nov. and distinguish it from the two species of Potamonemus are the following: the G1 TA of Buea gen. nov. is elongate (TA/SS 0.86) and is longer than that of Potamonemus (TA/SS 0.63); the first fourfifths of the G1 TA are straight and distinctly widened, with long bristle-like setae on the lateral margin ( Figure 7 View Figure 7 (a,d)) (vs slim along its entire length, and lacking bristle-like setae on the lateral margin in Potamonemus , Figure 7 View Figure 7 (b,c,e,f)); although short, the G2 TA of Buea gen. nov. (TA/SS 0.23, Figure 8 View Figure 8 (a)), is still longer than those of the two species of Potamonemus (TA/SS 0.13, Figure 8 View Figure 8 (b,c)); and the G2 TA of Buea gen. nov. has a pointed tip ( Figure 8 View Figure 8 (a)) (vs G2 TA of the two species of Potamonemus which has a blunt tip, Figure 8 View Figure 8 (b,c)).

Buea gen. nov. can be distinguished from the other genera of continental African potamonautines by differences in the carapace, G1, G2, third maxillipeds, and mandibles ( Cumberlidge 1993, 1994, 1999) ( Figures 1 – 3 View Figure 1 View Figure 2 View Figure 3 , 7 View Figure 7 (a – f) and 8(a – i)). Each of these genera has been recovered as a well-supported lineage in the most recent molecular studies of this fauna ( Daniels et al. 2006, fig. 1, 2015, fig. 2; Mvogo Ndongo et al. 2017c, fig. 1). Six of these genera are found in West and Central Africa ( Sudanonautesı Liberonautesı Potamonautesı Potamonemusı Louisea and Erimetopus ), and four have representatives in Cameroon ( Table 1 View Table 1 ) but only Louisea is endemic to that country (Cumberlidge 1999; Mvogo Ndongo et al. 2017a, 2017c, 2018).

Buea gen. nov. is superficially similar to Louisea , a genus of small freshwater crabs found in south-western Cameroon that also has a third maxilliped exopod lacking a flagellum. These two genera can be distinguished, however, by the length of the G1 TA: that of Buea gen. nov. is extremely long (TA/SS 0.86, Figure 7 View Figure 7 (a,d) (vs significantly shorter (TA/SS 0.31) in Louisea, Mvogo Ndongo et al. 2017a , fig. 3a,b; Mvogo Ndongo 2018, fig. 5a,b). In addition, the G1 TA of Buea gen. nov. curves outward ( Figure 7 View Figure 7 (a,d)) (vs S-shaped in Louisea, Mvogo Ndongo et al. 2017a , fig. 3a, b; Mvogo Ndongo 2018, fig. 5a,b), has a broadened mid-section that tapers to a pointed tip ( Figure 7 View Figure 7 (a,d)) (vs tube-like, ending in a blunt, rounded tip in Louisea, Mvogo Ndongo et al. 2017a , fig. 3A,B; Mvogo Ndongo 2018, fig. 5a,b); the G1 TA of Buea gen. nov. has long bristle-like setae on its lateral margin ( Figure 7 View Figure 7 (a,d)) (vs smooth, and lacking bristle-like setae in Louisea, Mvogo Ndongo et al. 2017a , fig. 3A,B; Mvogo Ndongo 2018, fig. 5a,b); and the G2 TA is relatively short (TA/SS 0.23, Figure 8 View Figure 8 (a)) (vs longer, TA/SS 0.64, in Louisea ( Mvogo Ndongo et al. 2017a, fig. 3C; Mvogo Ndongo 2018, fig. 5c).

Buea gen. nov. is superficially similar to two species of Sudanonautes ( S. orthostylis Bott, 1955 and S. tiko Mvogo Ndongo, Schubart, von Rintelen, Tamesse, and Cumberlidge, 2017b ) from south-western Cameroon, but can be distinguished from these two species as follows. The anterolateral margin of the carapace of Buea gen. nov. lacks a distinct intermediate tooth between the exorbital and epibranchial teeth ( Figure 1 View Figure 1 (a,b)) (vs a distinct intermediate tooth in S. orthostylis and S. tiko, Cumberlidge 1999 , fig. 31C), and the third maxilliped exopod lacks a flagellum ( Figure 8 View Figure 8 (d)) (vs an exopod with a long flagellum in S. orthostylis and S. tiko, Cumberlidge 1999 , fig. 34H; Mvogo Ndongo et al. 2017b, fig. 2d). In addition, both of these genera have a shortened G2 TA, whereas that of Buea gen. nov. is distinctly longer (TA/SS 0.23, Figure 8 View Figure 8 (a)) vs S. orthostylis and S. tiko (both with TA/SS 0.04) (Cumberlidge 1999, fig. 53V; Mvogo Ndongo et al. 2017b, fig. 3c).

The absence of a flagellum on the exopod of the third maxilliped can be used to distinguish Buea gen. nov. from Potamonautesı Erimetopus and Platythelphusa , and from most species of Liberonautes (except for L. grandbassa Cumberlidge, 1999 , and L. lugbe, Cumberlidge 1999 ) because these taxa possess a long flagellum on the exopod (Cumberlidge 1999; Cumberlidge et al. 1999; Cumberlidge and Reed 2004; Marijnissen et al. 2004). In addition, the short G2 TA of Buea gen. nov. (TA/SS 0.23; Figure 8 View Figure 8 (a)) can be used to distinguish it from Potamonautesı Erimetopusı Platythelphusa and Liberonautes because all possess a G2 with a long flagellumlike TA (TA/SS 0.33 – 0.75, Cumberlidge 1999, 2017; Cumberlidge et al. 1999; Marijnissen et al. 2004).

The updated freshwater crab species list for Cameroon now comprises 15 species in five genera assigned to the Potamonautinae : Louisea balssi ( Bott, 1959) , L. edeaensis ( Bott, 1969) , Potamonautes reidi Cumberlidge, 1999 , Potamonemus mambilorum Cumberlidge and Clark, 1992 , P. sachsi Cumberlidge, 1993 , Buea asylos ( Cumberlidge, 1993) comb. nov., Sudanonautes aubryi (H. Milne Edwards 1853) , S. africanus (A. Milne-Edwards 1869) , S. chavanesii (A. Milne- Edwards 1886), S. faradjensis ( Rathbun, 1921) , S. floweri ( De Man, 1901) , S. granulatus ( Balss, 1929) , S. monodi ( Balss, 1929) , S. orthostylis Bott, 1955 , and S. tiko Mvogo Ndongo et al. 2017b ( Cumberlidge and Clark 1992; Cumberlidge 1993, 1994, 1999; Mvogo Ndongo et al. 2017a, 2017b, 2017c, 2018).