Buea asylos ( Cumberlidge, 1993 ) 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 : 665-666

Buea asylos ( Cumberlidge, 1993) comb. nov.

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

Type species. Potamonemus asylos Cumberlidge, 1993 , by present designation.

Potamonemus asylos Cumberlidge, 1993: 576 – 584 , figs 3, 4, 5a – b, 6a – c, 8a – b; tables 2, 3; Cumberlidge 1999: figs 40C, 41C,F, 42C,F, 43C,F, 44C, 53G, 54 – 57, 61E, 65F, table IX; Ng et al. 2008: 171; Cumberlidge 2011a: 78, 80, 82, 86, table 6.1; Cumberlidge 2011b: 190; Mvogo Ndongo et al. 2017b: 3, table 1; Daniels et al. 2015, table 1.

Material examined

Type material. Cameroon: Buea asylos ( Cumberlidge, 1993) comb. nov. adult ♂ holotype, CW 27.6, CL 18.3, CH 9.0, FW 7.5 mm, between Buea (4.153484°N, 9.299551°E) and Kumba (4.638727°N, 9.441354°E), South-West Region, coll . R.H.L. Disney, 1969 ( NHM 1994.587 donation from NMU 1969 /1991) . Paratypes, 3 ♀♀, CWs 25.4, 23.7, 18.7 mm, 3 ♂♂, CWs 22.3, 20.1, 19.8 mm, between Buea (4.153484°N, 9.299551°E) and Kumba (4.638727°N, 9.441354°E), South-West Region, coll . R.H.L. Disney, 1969 ( NHM 1994.588 – 591 ), DNA voucher specimens ( Daniels et al. 2015, table 1) . Adult ♂, CW 22.4, CL 15.8, CH 6.8, FW 6.9 mm, Buea (4.153484°N, 9.299551°E) Kumba area, South-West Region, coll . R. H.L. Disney, 1969 ( NMU TRW 1969.22 ), specimen photographed here .

Other material examined. Adult ♀, CW 23.2, CL 17.2, CH 7.4, FW 7.4 mm, Buea (4.153484°N, 9.299551°E), Kumba area , South-West Region, coll . R.H.L. Disney, 29 April 1969 ( NMU TRW 1969.13 a) . Adult ♂, CW 19.8, CL 14.5, CH 6.8, FW 6.9 mm, 3 subadult ♂♂, CWs 16.4, 15.6, 14.9 mm, subadult ♀, CW 15.3 mm, 9 juv ., Okia Stream, Kumba area , South-West Region, coll . R.H.L. Disney, 9 May 1969 ( NMU TRW 1969.27 ) . Adult ♂, CW 19.0 mm, 3 subadult ♂♂, CWs 18.4, 15.8, 12.6 mm, subadult ♀, CW 17.9 mm, 2 juv . , Okia Stream, Kumba area , South-West Region, coll. R.H.L. Disney, 27 March 1969 ( NMU TRW 1969.29 ) . Limbé (formerly Victoria), South-West Region , 2 ♂♂, CWs 21.3, 20.1 mm, coll . E . Fickenday, 6 November 1912, ‘ edible land crabs ’ ( ZIM K-3607) .

Diagnosis

Exorbital tooth absent where anterolateral margin meets lateral orbital margin ( Figures 1 (a,b) and 4(a)); major cheliped dactylus broad, flattened, not arched ( Figures 1 (b) and 5(a,b)); lower margin of cheliped merus with four large jagged pointed teeth ( Figures 1 (b) and 6(a,b)); anterior corners of carapace surface smooth; carapace grooves shallow to absent ( Figures 1 (a) and 4(a); Cumberlidge 1993, figs. 2a, 3a).

Description

Same as for the genus and for P. asylos comb. nov. (see Cumberlidge 1993, 1999).

Distribution

Buea asylos comb. nov. is endemic to the rainforest zone of south-western Cameroon between the towns of Kumba, Buea and Limbé ( Cumberlidge 1993, 1999).

Type locality

Between Buea and Kumba, south-western Cameroon.

Ecology

Buea asylos comb. nov. is restricted to the humid lowland and montane rainforests of south-western Cameroon in the area near Mount Cameroon (4095 m asl) that has an annual average rainfall of more than 5000 mm ( Mvogo Ndongo et al. 2017a, 2017b).

Remarks

Significant morphological differences between B. asylos comb. nov., P. mambilorum and P. sachsi were found in the G1, G2 and mandible ( Figures 7 (a – f) and 8(a – c,g – i)) that are used here to define Buea gen. nov. Other noteworthy characters of B. asylos comb. nov. include those of the chelipeds and carapace of that set it apart from the two species of Potamonemus : the cheliped merus lower medial margin has large jagged teeth ( Figure 6 (a,b)) (vs small granules in Potamonemus , Figure 6 (c,f)), the cheliped carpus medial margin of B. asylos comb. nov. has a small but distinct pointed proximal tooth ( Figure 5 (g)) (vs a small granule-sized tooth in Potamonemus , Figure 5 (h,i)), the cheliped dactylus is distinctly broadened ( Figures 1 (b) and 5 (a)) (vs distinctly slim or arched in Potamonemus , Figure 5 (c,e)), and the carapace proportions of B. asylos comb. nov. are wider (CW/FW 3.35, vs 3.08 – 3.12), longer (CW/FW 2.32, vs 2.22 – 2.25), and higher (CW/FW 1.10, vs 0.96 – 1.07) than in Potamonemus .

Conservation status

The extinction risk status of B. asylos comb. nov. was assessed in 2008 using the International Union for the Conservation of Nature (IUCN) Red List protocols ( Cumberlidge 2008a) as Data Deficient (DD) in view of the lack of information on its extent of occurrence (EOO), ecological requirements, population size, population trends and long-term threats ( Cumberlidge 1993, 2011a, 2011b; Cumberlidge et al. 2009; IUCN 2012). The three locations available in this study give a recalculated EOO of 142 km 2, and an area of occupancy (AOO) of 12 km 2, using GeoCAT (http://geocat.kew.org; Bachman et al. 2011), but these are still probably underestimates given the paucity of the locality data (but if taken alone would point to a Red List threatened category). The extinction risk status of P. mambilorum (seven locations, EOO 43,291 km 2; Cumberlidge 2008b) and P. sachsi (four locations, EOO 24,219 km 2; Cumberlidge 2008c) were assessed in 2008 ( Cumberlidge 2008b, 2008c) as Least Concern (LC) and Vulnerable (VU), respectively, ( Cumberlidge 1993, 2011a, 2011b; Cumberlidge et al. 2009; IUCN 2012). Although the recalculations of the EOO and the AOO for these three species do not in themselves warrant a reassessment of their extinction risk, there is reason to believe that the threat status of these species may have intensified since the last assessment. For example, recent field work in the wetland ecosystems of the South-West and Littoral regions of Cameroon by the second author indicates that these habitats are being impacted by deforestation and by intensive agricultural practices that are severely altering the flow patterns of small streams and impacting the aquatic biodiversity ( Mvogo Ndongo et al. 2017a, 2017b, 2017c, 2018). Awareness of these current threats to the habitats of B. asylos comb. nov., P. mambilorum and P. sachsi means that each of these taxa is likely to be reassigned to a more threatened category once new IUCN Red List extinction risk assessments have been carried out. There is a need for further field research specifically aimed at gathering the data needed for an extinction risk assessment of these littleknown endemic species from this understudied biodiversity hotspot.

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 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 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.