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

Cumberlidge, Neil, Mvogo Ndongo, Pierre A., Clark, Paul F. & Daniels, Savel R., 2019, 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, Journal of Natural History 53 (11), pp. 659-676 : 662-664

Buea gen. nov.

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

Potamonemus – 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 (d)). Lower margin of cheliped merus with large pointed tooth distally ( 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 (a,d)); G1 SS basal margin very wide, 5× that of distal margin ( Figure 7 (a,d)); G2 TA distinctly short (TA/SS 0.23) with pointed tip ( 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 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 (a,d)) (vs slim along its entire length, and lacking bristle-like setae on the lateral margin in Potamonemus , Figure 7 (b,c,e,f)); although short, the G2 TA of Buea gen. nov. (TA/SS 0.23, Figure 8 (a)), is still longer than those of the two species of Potamonemus (TA/SS 0.13, Figure 8 (b,c)); and the G2 TA of Buea gen. nov. has a pointed tip ( Figure 8 (a)) (vs G2 TA of the two species of Potamonemus which has a blunt tip, 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 , 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 ) 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 (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 (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 (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 (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 (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 (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 (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 (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 (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).

Figures

Figure 1. Buea asylos (Cumberlidge, 1993) comb. nov., holotype, adult ♂ CW 27.6 mm, between Buea and Kumba, Cameroon (NHM 1994.587). (a) Whole animal, dorsal view; (b) whole animal, ventral view. Photographs by Phillip Crabb, NHM, London. Scale bar: a = 14 mm; b = 10 mm.

Figure 2. Potamonemus mambilorum Cumberlidge and Clark, 1992, holotype, adult ♂, CW 34.5 mm, Somié, Cameroon (NHM 1991:183). (a) Whole animal, dorsal view; (b) whole animal, ventral view. Photographs by Phillip Crabb, NHM, London. Scale bar: a = 21 mm; b = 28 mm.

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.

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.

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.

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.