Potamonemus man, Ndongo & Rintelen & Cumberlidge, 2021

Ndongo, Pierre A. Mvogo, Rintelen, Thomas von & Cumberlidge, Neil, 2021, A new species of the freshwater crab genus Potamonemus Cumberlidge & Clark, 1992 (Crustacea, Potamonautidae) endemic to the forested highlands of southwestern Cameroon, Central Africa, ZooKeys 1017, pp. 127-141 : 127

publication ID	https://dx.doi.org/10.3897/zookeys.1017.60990
publication LSID	lsid:zoobank.org:pub:36B25C08-43C8-4622-9189-B4F692651CFB
persistent identifier	https://treatment.plazi.org/id/58FD0C15-4CB9-4561-8453-B98255BBEE25
taxon LSID	lsid:zoobank.org:act:58FD0C15-4CB9-4561-8453-B98255BBEE25
treatment provided by	ZooKeys by Pensoft
scientific name	Potamonemus man
status	sp. nov.

Treatment

Potamonemus man sp. nov. Figures 1d View Figure 1 , 2d View Figure 2 , 3d View Figure 3 , 4d View Figure 4 , 5g, h, l View Figure 5 , 6j-l View Figure 6 , 7d, h Common name: Man Lake freshwater crab View Figure 7

Holotype.

Adult ♂ (CW 24.51 mm, CL 17.09 mm, CH 9.62 mm, FW 7.62 mm), Cameroon, Southwest Region, Mount Manengouba Ecological Reserve, Man Lake, Mount Manengouba (5.02414, 9.82142), 1,958 m a.s.l., 14 March 2017, coll. P.A. Mvogo Ndongo (ZMB Crust. 30320).

Paratypes.

1 adult ♂ (CW 21.37 mm, CL 15.61 mm, CH 8.45 mm, FW 6.69 mm), 1 adult ♀ (CW 23.55 mm, CL 16.87 mm, CH 10.09 mm, FW 7.60 mm), Cameroon, Southwest Region, Mount Manengouba Ecological Reserve, Man Lake, Mount Manengouba (5.03604, 9.82906), 1,958 m a.s.l., 14 March 2017, coll. P.A. Mvogo Ndongo (ZMB Crust. 30324). 2 adult ♂ (CW 20.12 mm, CL 14.64 mm, CH 7.92 mm, FW 6.76 mm; CW 20.40 mm, CL 14.73 mm, CH 8.16 mm, FW 6.63 mm); 3 subadult ♂ (CW 18.46 mm, CL 13.89 mm, CH 7.40 mm, FW 6.16 mm; CW 19.38 mm, CL 13.78 mm, CH 7.78 mm, FW 6.63 mm; CW 14.05 mm, CL 10.67 mm, CH 5.84 mm, FW 5.30 mm), Cameroon, Southwest Region, Mount Manengouba Ecological Reserve, Man Lake, Mount Manengouba (5.03604, 9.82906), 1,958 m a.s.l., 14 March 2017, coll. P.A. Mvogo Ndongo (IFAS-017); 4 adult ♀ (CW 19.39 mm, CL 14.07 mm, CH 7.74 mm, FW 6.48 mm; CW 17.37 mm, CL 12.46 mm, CH 6.94 mm, FW 6.33 mm; CW 16.88 mm, CL 12.06 mm, CH 6.36 mm, FW 5.20 mm), Cameroon, Mount Manengouba Ecological Reserve, Man Lake, Mount Manengouba (5.03604, 9.82906), 1,958 m a.s.l., 14 March 2017, coll. P.A. Mvogo Ndongo (IFAS-018).

Other material.

Bakossi National Park (Figs 1c View Figure 1 , 2c View Figure 2 , 3c View Figure 3 , 4c View Figure 4 , 5e, f, j View Figure 5 , 6g-i View Figure 6 , 7c, g View Figure 7 ). 1 adult ♂ (CW 30.41 mm, CL 20.57 mm, CH 12.50 mm, FW 9.32 mm) , 1 adult ♀ (CW 27.48 mm, CL 20.06 mm, CH 11.31 mm, FW 8.19 mm), Cameroon, Southwest Region, Bakossi National Park (5.031083, 9.687528), 1,253 m a.s.l., 15 March 2017, coll. P. A. Mvogo Ndongo (ZMB Crust. 30328) GoogleMaps . 5 adult ♂ (CW 27.61 mm, CL 19.37mm, CH 11.39 mm, FW 8.65 mm; CW 26.54 mm, CL 19.09 mm, CH 10.80 mm, FW 9.13 mm; CW 25.55 mm, CL 18.68 mm, CH 10.58 mm, FW 8.41 mm; CW 25.3 mm, CL 18.05 mm, CH 10.70, FW 8.41 mm) (IFAS-014) ; 2 subadult ♂ (CW 22.17 mm, CL 15.76 mm, CH 9.04 mm, FW 7.35 mm; CW 22.02 mm, CL 15.67 mm, CH 9.06 mm, FW 7.49 mm; CW 22.04 mm, CL 16.00 mm, CH 9.22 mm, FW 7.65 mm; CW 21.35 mm, CL 15.19 mm, CH 8.76 mm, FW 6.81 mm), Cameroon, Southwest Region, Bakossi National Park (5.031083, 9.687528), 1,248 m a.s.l., 15 March 2017, coll. P.A. Mvogo Ndongo (IFAS-015) GoogleMaps . 2 subadult ♀ (CW 23.76 mm, CL 17.57 mm, CH 9.88 mm, FW 7.68 mm; CW 23.31 mm, CL 16.63 mm, CH 9.08 mm, FW 7.59 mm), Cameroon, Southwest Region, Bakossi National Park (05.031083, 9.687528), 1,248 m a.s.l., 15 March 2017, coll. P.A. Mvogo Ndongo (IFAS-016) GoogleMaps .

Diagnosis.

Carapace anterior surface smooth except for faint urogastric groove (Fig. 1d View Figure 1 ). Broad epimeral (longitudinal) suture on carapace sidewall (branchiostegite) dividing carapace sidewall into 2 regions, vertical (pleural) groove lacking (Fig. 1d View Figure 1 ). Outer lower margin of cheliped merus lined by small, blunt teeth, inner lower margin smooth, distal meral tooth distinct, pointed (Fig. 3d View Figure 3 ). Major chela dactylus straight (not arched) (Fig. 5g View Figure 5 ). Sternal sulcus S2/S3 completely traversing sternum; S3/S4 incomplete, reduced to 2 short, distinct notches on each side of sternum (Fig. 3d View Figure 3 ). G1 with long TA (TA/SS 0.66), slim, curving outward, lacking marginal setae, tapering to pointed tip; G2TA remarkably short (TA/SS 0.13) (Fig. 6j, l View Figure 6 ). A small species, mature between CWs 20-25 mm.

Description.

Carapace ovoid, medium height (CH/FW 1.17), wide (CW/FW 3.19); carapace surface smooth; postfrontal crest distinct, completely traversing carapace, lateral ends meeting anterolateral margins (Fig. 1d View Figure 1 ); exorbital tooth low, distinct; intermediate, epibranchial teeth each reduced to small granule (Fig. 4d View Figure 4 ); anterolateral margin behind epibranchial tooth smooth (Fig. 4d View Figure 4 ). Carapace branchiostegite with prominent epimeral suture dividing wall into subhepatic/suborbital, pterygostomial regions; vertical (pleural) suture faint (Fig. 3d View Figure 3 ). Sternal sulcus S2/S3 deep, completely traversing sternum; S3/S4 incomplete, reduced to 2 short, distinct notches on each side of sternum (Fig. 3d View Figure 3 ); margins of S3, S4 raised, broad (Fig. 3d View Figure 3 ); episternal sulci S4/E4, S5/E5, S6/E6 faint or missing, S7/E7 complete (Fig. 3d View Figure 3 ). Mandibular palp 2-segmented; medium-sized anterior lobe at junction between segment (0.25 × TS length; Fig. 7h View Figure 7 ). Third maxillipeds filling entire buccal cavern, except for transversely oval, efferent respiratory openings in superior lateral corners; ischium smooth, lacking vertical groove; exopod lacking flagellum (Fig. 7d View Figure 7 ).

Male chelipeds greatly unequal, right cheliped larger than left (Figs 1d View Figure 1 , 5g, h View Figure 5 ). Movable finger (dactylus), fixed finger (pollex of propodus) of right (major) chela both slim, elongated; fixed finger with 3 large pointed teeth (2 proximal, 1 distal); movable finger relatively stout, straight (not highly arched), with 4 small but distinct teeth (2 proximal, 2 distal; Fig. 5g View Figure 5 ). Left (minor) chela dactylus, propodus smaller than right chela, with small teeth on occluding margins (Fig. 5h View Figure 5 ). Inner inferior margin of cheliped merus lined by small teeth, outer inferior margin smooth; distal meral tooth large, pointed (Fig. 5d View Figure 5 ). Cheliped carpus inner margin with large pointed distal tooth; proximal tooth much smaller, followed by granule (Fig. 5l View Figure 5 ). Ambulatory legs (P2-5) slender, P4 longest, P5 shortest; dactyli P2-5 tapering to point, each bearing rows of downward-pointing sharp bristles, P5 dactylus shortest (Fig. 1d View Figure 1 ).

Male pleon triangular, margins not indented and lacking setae (Fig. 3d View Figure 3 ). G1 with long TA (TA/SS 0.66), slim, curving outward, lacking marginal setae, tapering to pointed tip; G2TA remarkably short (TA/SS 0.13) (Fig. 6j, l View Figure 6 ); G1SS, broad in basal, midsection, distal quarter tapering sharply, narrow at junction with G1TA (Fig. 6j, l View Figure 6 ). G2TA extremely short (G2TA/SS 0.3; Fig. 6k View Figure 6 ).

Adult female. Right and left chelipeds subequal. Fixed, movable fingers of chela interspersed with series of smaller acute teeth along their length. Pleon wide, covering entire sternum, reaching bases of coxae of P2-5; pleon with 6 free pleomeres (A1-6) becoming gradually wider proximally, telson wide, forming near semicircle.

Size. Small species, CW in mature individuals ranging from 20.0-30.4 mm.

Colour in life. Dorsal carapace and all ambulatory legs dark brown, chelipeds red.

Type locality.

Stream flowing into Man Lake, Mount Manengouba, in Manengouba Ecological Reserve, Southwest Region of Cameroon.

Etymology.

The species is named for Man Lake, one of a pair of small lakes in the caldera at the summit of Mount Manengouba (the other lake being Woman Lake). The species epithet is used as a noun in apposition.

Habitat.

At the Man Lake locality at the summit of Mount Manengouba the species is found in a small stream flowing into the lake, and it was also collected from a small stream in the Bakossi National Park. Both of these localities are located in rainforest habitat found along the Cameroon Volcanic Line, a 1,600 km long chain of volcanoes that stretches from the islands in the Gulf of Guinea to the mountains of eastern Nigeria and western Cameroon, including Mount Cameroon.

Remarks.

The new species is assigned to Potamonemus because it conforms to the genus diagnosis ( Cumberlidge and Clark 1992; Cumberlidge 1993c; Cumberlidge et al. 2019). Potamonemus man sp. nov. most closely resembles P. sachsi in that the dactylus of the major cheliped of both species is straight rather than highly arched. These two species can be distinguished from each other by the smooth carapace and branchiostegal sidewalls in P. man sp. nov. (Figs 1D View Figure 1 , 2D View Figure 2 ) (vs. patches of short setae along the anterolateral and posterolateral margins of the carapace that continue around to the sidewalls in the subhepatic and pterygostomial regions of the branchiostegite in P. sachsi ( Cumberlidge et al. 2019: fig. 4c)). The highly arched dactylus of the major cheliped of P. mambilorum distinguishes it from both P. man sp. nov. and P. sachsi . Finally, P. man sp. nov. can be distinguished from P. mambilorum and P. sachsi by the body size of adult specimens: the new species and P. sachsi are adult between CW 20-30 mm and CW 23-28 mm, respectively, while P. mambilorum is the largest species (adult at CW 29-38 mm).

A phylogenetic tree (Fig. 8 View Figure 8 ), based on 1,848 base pairs representing the combined partial sequences of three mtDNA markers (COI, 16S RNA, and 12S RNA), recovered three species of Potamonemus as a single clade with strong BI and ML confidence values (1/100 at this node). The three species of Potamonemus ( P. mambilorum , P. man sp. nov., and P. sachsi ) form an independent lineage within the subfamily Potamonautinae , and all are found in the same geographical area of Cameroon. The uncorrected p -distance between Potamonemus man sp. nov. and P. mambilorum is 2.2% for 12S RNA and 0.6% for 16S RNA, and between P. man sp. nov. and P. sachsi it is 4.5% for 12S RNA and 4.6% for 16S RNA.

Conservation.

Potamonemus man sp. nov. is found in an area of great conservation interest. The aquatic habitats of this species in the Mount Manengouba Ecological Reserve and in the Bakossi National Park are both in montane tropical rainforest in the Cameroon highlands, an area with a high biodiversity and a high rate of endemism, including freshwater crabs ( Cumberlidge et al. 2019; Mvogo Ndongo et al. 2017a, d, c, 2018, 2019, 2020). In Mount Manengouba Ecological Reserve the small, forested stream near Man Lake where P. man sp. nov. lives also supports a sympatric population of the endangered freshwater crab Louisea balssi (Bott, 1959). Significantly, there are no reports of any species of invertebrates (molluscs, insects, crustaceans) or vertebrates (fish, amphibians, snakes, and birds) from Man Lake itself. This inhospitality to life may be related to the unusual green colour of its waters which may be due to the accumulation of lethal compounds, which may also be a potential danger to humans (see Mvogo Ndongo et al. 2018). Both the Mount Manengouba Ecological Reserve and the Bakossi National Park are under increasing pressure from growing nearby human populations and from the associated clearance of land for agriculture. As a result, despite being found in protected areas, the habitat of P. man sp. nov. is increasingly threatened by nearby intensive agricultural practices and forest destruction for firewood collection. In addition, the farmers encroaching on these habitats use agrochemicals and pesticides on their crops, and these pollutants eventually drain into the aquatic systems, potentially poisoning the freshwater communities ( Mvogo Ndongo et al. 2018).