BRACHYURA Latreille, 1802

Cumberlidge, Neil & Clark, Paul F., 2018, Albertine Rift Valley endemics: three new species of freshwater crabs (Brachyura: Potamoidea: Potamonautidae) from Uganda, the Democratic Republic of the Congo, and Rwanda, Journal of Natural History 52 (25 - 26), pp. 1637-1656 : 1639-1649

Infraorder BRACHYURA Latreille, 1802

Superfamily POTAMOIDEA Ortmann, 1896 Family POTAMONAUTIDAE Bott, 1970 Subfamily Potamonautinae Bott, 1970

Genus Potamonautes MacLeay, 1838

Potamonautes bwindi sp. nov.

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

Material examined

Type material. Uganda. Holotype (here designated): adult ♂, CW 20.2 , CL 13.7 , CH 6.8 , FW 6.8 mm, from upper reaches of Mbwa River in the Bwindi Impenetrable National Park , Kayonza area , Gombolola , Kigezi, Western Uganda, − 0.98333°S, 29.68333°E, in dense forest, clean river water, 14.4°C, 1615 m asl, coll . A .W.R . McCrae, 21 September 1962 ( NHMUK reg. 2018. 1) . Paratypes: three adult ♀♀, CW 22.6 , CL 15 ; CW 21 , CL 14.6 ; CW 20.6 , CL 16 mm, two subadult ♂♂, CW 18.7 , CL 13.3 ; CW 17.9 , CL 12 mm, all same data as holotype ( NHMUK reg. 2018. 2 – 4) .

Diagnosis

Based on holotype (adult ♂ CW 20.2). Carapace: postfrontal crest faint but complete, lateral ends meeting anterolateral margins; epigastric crests rounded distinctly raised; exorbital, epibranchial teeth reduced to granules; anterolateral margin posterior to epibranchial tooth smooth ( Figures 1a , 4a ). Third maxilliped: ischium smooth, lacking sulcus ( Figures 1b , 4a ); s3/ s4 incomplete, comprising two long deep grooves on lateral margins, otherwise smooth; margins of s4 low, not raised ( Figure 1b ). Cheliped: dactylus (moveable finger) slim, highly arched, enclosing oval interspace, one medium tooth in mid-section, other teeth small; propodus (fixed finger) with large molar proximally ( Figure 5a ); carpus distal tooth large, pointed, proximal tooth small, low ( Figure 5d ); merus lined by series of small teeth, distal meral tooth large, pointed. G1 terminal article: first third straight in line with longitudinal axis of subterminal segment, median part directed outward at 45°, widened by raised rounded ventral lobe ( Figure 6d), tip curving sharply upwards ( Figure 6a,d).

Description

Based on holotype (adult ♂ CW 20.2 ) . Carapace : medium height ( CH / FW 1.0), front broad, measuring one-third CW ( FW / CW 0.33); semi-circular, urogastric, cardiac, posterior, cervical carapace grooves all distinct; postfrontal crest complete, faint, lateral ends meeting epibranchial teeth; epigastric crests faint, median sulcus between crests short, forked posteriorly; exorbital, epibranchial teeth each reduced to granule; anterolateral margin between exorbital, epibranchial teeth smooth, curving slightly outward, lacking intermediate tooth; anterolateral margin posterior to epibranchial tooth smooth ( Figure 1a ); vertical sulcus on carapace branchiostegal wall faint, meeting longitudinal sulcus, dividing carapace wall into three parts; suborbital margin granulated ( Figure 1b ) . Third maxilliped: exopod with long flagellum, ischium smooth lacking vertical groove ( Figure 4a ). Epistomial tooth large, triangular, margins lined by large round granules ( Figure 4a ). Mandible: palp two-segmented; terminal segment simple. Sternum: s2/s3 deep, completely crossing sternum; s3/s4 incomplete, comprising two long deep grooves on lateral margins, otherwise smooth; margins of s4 low, not raised ( Figure 1b ). Cheliped: adult male dactylus (moveable finger) slim, highly arched, enclosing oval interspace, one medium tooth in mid-section, other teeth small; propodus (fixed finger) with large molar proximally ( Figure 5a ); carpus distal tooth large, pointed, proximal tooth small, low ( Figure 5d ); merus lined by series of small granules, distal meral tooth large, pointed; superior surface granulated. Pleon: outline broadly triangular with straight margins. G1: terminal article directed outward, proximal third straight in line with longitudinal axis of subterminal segment, median part directed outward at 45°, widened by raised rounded ventral lobe, tip curving sharply upwards ( Figure 6a,d). G2: terminal article long, flagellumlike ( Figure 7a ). Small species, adult at CW 20 mm .

Distribution

Uganda. This species is known only from a single locality in the upper reaches of the Mbwa River in the Bwindi Impenetrable National Park , Kayonza area , Gombolola , Virunga Massif, Western Uganda (− 0.98333°S, 29.68333°E; Figure 8a ) .

Type locality

Upper reaches of Mbwa River in the Bwindi Impenetrable National Park , Kayonza area , Gombolola , Kigezi, Western Uganda (− 0.98333°S, 29.68333°E), in dense forest, clean river water, 14.4°C, 1615 m asl .

Conservation status

An IUCN conservation assessment of P. bwindi sp. nov. has not yet been carried out, but given the fact that this species is known from only six specimens that are all from a single locality in a protected area (Bwindi Impenetrable National Park), and that no threats are known, it would probably be regarded as Data Deficient.

Ecology

This species was collected from a high-altitude locality (1615 m asl) in dense transitional/ intermediate montane forest from the clean, cool waters (14.4°C) of the upper reaches of Mbwa River in the Bwindi Impenetrable National Park. This national park is part of the Lake Victoria Basin Freshwater Ecoregion 521 ( Thieme et al. 2005; Abell et al. 2008). The

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Mbwa River is a tributary of the Ishasha River that flows north into Lake Rutanzige which is part of the Nile River basin. This remote national park is mostly accessible only on foot and is part of the Bwindi Impenetrable Forest that borders the Virunga National Park in the DRC. This is the first record of an endemic species of freshwater crab from the Bwindi Impenetrable National Park.

Etymology

The new species is named for the Bwindi Impenetrable National Park which lies in southwestern Uganda where this species was first collected. The specific epithet bwindi is used as a Latin noun in apposition. The vernacular name is the Bwindi crab.

Remarks

Potamonautes bwindi sp. nov. differs from P. kivu sp. nov. and P. rwenzori sp. nov. in that the distal tooth on the merus of the cheliped is large and pointed followed by a row of small teeth ( Figure 1a,b ) [vs either a small and pointed distal meral tooth ( P. kivu sp. nov.), or a blunt and low distal meral tooth ( P. rwenzori sp. nov.), followed by a row of granules in P. kivu sp. nov. and P. rwenzori sp. nov.; Figures 2b and 3b ]; and the cheliped dactylus of the adult male is highly arched and encloses a broad oval interspace when closed ( Figure 5a ) (vs a cheliped dactylus of the adult male that is slightly curved, not arched, and encloses a long narrow interspace in P. kivu sp. nov. and P. rwenzori sp. nov.; Figure 5b,c ).

Potamonautes bwindi sp. nov. differs from other, similar small-bodied species of freshwater crabs found in Uganda in that s3/s4 ( Figure 2a ) comprises two long deep grooves at the margins and is otherwise faint or absent (vs two short shallow grooves at the margins in P. elgonensis Cumberlidge and Clark, 2010a and P. kanstyore Cumberlidge and Clark, 2017 ); the third maxilliped ischium is smooth and lacks a vertical sulcus ( Figure 2a ) (vs a third maxilliped ischium with a deep vertical sulcus in P. loveni ( Colosi, 1924) , P. mutandensis , P. rukwanzi Corace, Cumberlidge and Garms, 2001 , and P. williamsi Cumberlidge and Clark, 2010a ); the cheliped merus has a large pointed distal meral tooth ( Figure 1a ) (vs a small, low distal meral tooth in P. elgonensis , P. imatongensis Cumberlidge and Clark, 2016 ; P. loveni , P. morotoensis Cumberlidge and Clark, 2016 ; P. rukwanzi and P. williamsi ); the distal tooth on the cheliped carpus is small, broad and low ( Figure 5d ) (vs a large, pointed distal tooth in the cheliped carpus in P. busungwe Cumberlidge and Clark, 2017 , P. entebbe Cumberlidge and Clark, 2017 ; P. imatongensis and P. kantsyore Cumberlidge and Clark, 2017 ); and the tip of the G1 terminal article curves sharply upwards ( Figure 6a,d) (vs a G1 terminal article with either a straight or a slightly upturned tip in P. busungwe , or a straight tip in P. amalerensis ( Rathbun, 1935) , P. busungwe , P. elgonensis , P. entebbe , P. imatongensis , P. loveni , P. morotoensis and P. mutandensis (cf. Cumberlidge and Clark 2010a, 2010b, 2016, 2017; Cumberlidge and Meyer 2011).

Figures

Figure 1. Potamonautes bwindi sp. nov., holotype, adult male, CW 20.2 mm, Bwindi Impenetrable Forest, Uganda (NHMUK 2018. 1). (a) Whole animal, dorsal view; (b) whole animal, ventral view.

Figure 2. Potamonautes kivu sp. nov., holotype, adult male, CW 24.9 mm, Gisenyi, Lake Kivu, Rwanda (NHMUK reg. 2018. 5). (a) Whole animal, dorsal view; (b) whole animal, ventral view.

Figure 3. Potamonautes rwenzori sp. nov., holotype, adult male, CW 24.3 mm, Maya Moto, Rwenzori Mountains, Democratic Republic of the Congo (NHMUK 2018. 6). (a) Whole animal, dorsal view; (b) whole animal, ventral view. Photographs by Phillip Crabb, Natural History Museum, UK.

Figure 4. Frontal view of carapace. (a) Potamonautes bwindi sp. nov., holotype, adult male, CW 20.2 mm, Bwindi Impenetrable Forest, Uganda (NHMUK 2018. 1); (b) Potamonautes kivu sp. nov., holotype, adult male, CW 24.9 mm, Gisenyi, Lake Kivu, Rwanda (NHMUK reg. 2018. 5); (c) Potamonautes rwenzori sp. nov., holotype, adult male, CW 24.3 mm, Maya Moto, Rwenzori Mountains, Democratic Republic of the Congo (NHMUK 2018. 6). Photograph c by Phillip Crabb, Natural History Museum, UK.

Figure 5. Frontal view of left and right chelipeds.(a) Potamonautes bwindi sp. nov.,holotype, adult male, CW 20.2 mm, Bwindi Impenetrable Forest, Uganda (NHMUK 2018. 1). (b) Potamonautes kivu sp. nov., holotype, adult male, CW 24.9 mm, Gisenyi, Lake Kivu, Rwanda (NHMUK reg. 2018. 5); (c) Potamonautes rwenzori sp. nov., holotype, adult male, CW 24.3 mm, Maya Moto, Rwenzori Mountains, Democratic Republic of the Congo (NHMUK 2018. 6). Dorsal view of right cheliped carpus. (d) Potamonautes bwindi sp. nov., holotype, adult male, CW 20.2 mm, Bwindi Impenetrable Forest, Uganda (NHMUK 2018. 1). (e) Potamonautes kivu sp. nov., holotype, adult male,CW 24.9 mm, Gisenyi,Lake Kivu,Rwanda (NHMUK reg. 2018. 5). (f) Potamonautes rwenzori sp. nov., holotype, adult male, CW 24.3 mm, Maya Moto, Rwenzori Mountains,Democratic Republic of the Congo (NHMUK 2018.6).Scale bars:a = 5.48 mm;b = 6.7 mm;c = 4.4 mm. Size of d–f scaled for comparison. Photograph c by Phillip Crabb, Natural History Museum, UK.

Figure 7. G2 ventral view (a–c). (a) Potamonautes bwindi sp. nov., holotype, adult male, CW 20.2 mm, Bwindi Impenetrable Forest, Uganda, total length G2 4.68 mm (terminal article 1.6 mm, subterminal segment 3.08 mm, NHMUK 2018. 1). (b) Potamonautes kivu sp. nov., holotype, adult male, CW 24.9 mm, Gisenyi, Lake Kivu, Rwanda (NHMUK reg. 2018. 5), total length G2 6.52 mm (terminal article 2.2 mm, subterminal segment 4.32 mm (c) Potamonautes rwenzori, adult male, CW 24.3 mm, Maya Moto, Rwenzori Mountains, Democratic Republic of the Congo, total length G2 7.1 mm (terminal article 2.5 mm, subterminal segment 4.6 mm; NHMUK 2018. 6).

Figure 8. Distribution map showing the known localities of Potamonautes bwindi sp. nov. (black circle, not shown to scale); Potamonautes kivu sp. nov. (black star, not shown to scale); Potamonautes rwenzori sp. nov. (black squares, not shown to scale) in Uganda and the Democratic Republic of the Congo. For exact localities see text.