Potamonautes rwenzori, Cumberlidge & Clark, 2018

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 : 1652-1655

publication ID	https://doi.org/ 10.1080/00222933.2018.1480812
publication LSID	lsid:zoobank.org:pub:FC681BD6-6FB2-4A14-B068-89FC3EB26605
persistent identifier	https://treatment.plazi.org/id/4F58C651-FF8B-6352-FE3A-29ADB305FD50
treatment provided by	Felipe
scientific name	Potamonautes rwenzori
status	sp. nov.

Treatment

Potamonautes rwenzori View in CoL sp. nov.

( Figures 3a,b View Figure 3 , 4c View Figure 4 , 5c,f View Figure 5 , 6c,f, 7c View Figure 7 , 8c View Figure 8 )

Material examined

Type material. Democratic Republic of the Congo. Holotype (here designated): adult ♂, CW 24.3 , CL 16.7 , CH 8.9 , FW 7.3 mm, from River Talya , Maya Moto , near Mutsora (a station in the Virunga National Park , formerly the Albert National Park), western foothills of the Rwenzori Mountains, 0.316728°N, 29.750125°E 1100 – 1200 m asl, date and coll GoogleMaps . unknown ( NHMUK reg. 2018. 6, pres. the Royal Belgian Institute of Natural Sciences , Brussels, Belgium) . Paratypes: 2 adult ♂♂, CW 21.4 , CL 15.3 ; CW 23.2 , CL 16.1 , 2 adult ♀♀, CW 24 , CL 17.5 ; CW 21.3 , CL 15.9 mm, same details as holotype ( NHMUK reg. 2018. 7 – 8), 0.316728°N, 29.750125° E GoogleMaps .

Other material. Uganda. Adult ♂, CW 25.8 , CL 17.5 mm; three subadult ♂♂, CW 19.2 , CL 14.3 ; CW 18.8 , CL 13.8 ; CW 17.8 , CL 12.7 ; three adult ♀♀, CW 24.3 , CL 17.1 ; CW 21.4 , CL 16.1 ; CW 20.5 , CL 15.2 , Rwenzori Mountains, 0.239081°N, 29.942965°E, coll GoogleMaps . unknown, 1 November 1952 ( NHMUK reg. 2018. 9 – 15) .

Diagnosis

Carapace: medium height ( CH /FW 1.2); exorbital, epibranchial teeth each reduced to granule, postfrontal crest complete, faint medially, lateral ends well defined, meeting epibranchial teeth; anterolateral margin posterior to epibranchial tooth finely serrate, almost smooth ( Figure 3a View Figure 3 ); vertical sulcus on carapace branchiostegal wall faint, meeting longitudinal sulcus, dividing carapace wall into three parts not meeting anterolateral margin ( Figure 4c View Figure 4 ). Third maxilliped: ischium with vertical sulcus; s3/s4 complete, deep. Cheliped: inferior margins of merus with series of small granules, distal meral tooth small; propodus (fixed finger) of major cheliped with large teeth along cutting edge, largest molars proximal; dactylus (movable finger) with series of small teeth along cutting edge interspersed by two medium-sized teeth in middle, not arched, enclosing long narrow interspace when closed ( Figure 5c View Figure 5 ); carpus distal tooth large, pointed, proximal tooth small, pointed ( Figure 5f View Figure 5 ). G1: terminal article straight, entire terminal article directed outwards at 45° to longitudinal axis of subterminal segment, median part widened slightly by low slim ventral lobe ( Figure 6f), tip slightly upturned ( Figure 6c,f).

Description

Carapace: medium height ( CH /FW 1.2); front broad, measuring one-third CW (FW/CW 0.3); semi-circular, urogastric, cardiac, posterior, cervical carapace grooves all faint; postfrontal crest complete, faint, lateral ends well defined meeting epibranchial teeth; epigastric crests distinct, 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 3a View Figure 3 ); vertical sulcus on carapace branchiostegal wall distinct, incomplete, beginning at longitudinal sulcus not meeting anterolateral margin, dividing carapace branchiostegal wall into three parts; suborbital margin smooth. Third maxilliped: exopod with long flagellum, ischium with distinct vertical sulcus. Epistomial tooth: large, triangular, margins lined by faint granules ( Figure 3b View Figure 3 ). Mandible: palp two-segmented, terminal segment simple. Sternum: s2/s3, s3/s4 deep, wide, both completely crossing sternum; s4/e4, s5/e5, s6/e6, s7/e7 all faint ( Figure 3b View Figure 3 ). Cheliped: propodus (fixed finger) of adult male with series of small, medium sized teeth along cutting edge interspersed by two large pointed teeth in middle; dactylus (movable finger) with series of small teeth along cutting edge interspersed by two medium sized teeth in middle, not arched, enclosing long narrow interspace when closed ( Figure 5c View Figure 5 ); inferior margins of merus with series of small rounded teeth, distal tooth small, low; distal tooth on inner margin of carpus large, pointed, proximal tooth very small, granular ( Figure 5f View Figure 5 ), superior surface of merus granulated. Pleon: outline broadly triangular with straight margins. G1: terminal article straight, entire terminal article directed outwards at 45° to longitudinal axis of subterminal segment, median part widened slightly by low slim ventral lobe, tip slightly upturned ( Figure 6c, f). G2: terminal article long, flagellum-like ( Figure 7c View Figure 7 ). Small-sized species, adult size range between CW 20.5 – 25.8 mm.

Distribution

This species is found in the Rwenzori Mountains from two localities, one in the western foothills of the Rwenzori Mountains in the DRC, and one in the central and eastern parts of the Rwenzori Mountains in Uganda ( Figure 8c View Figure 8 ).

Type locality

DRC, River Talya , Maya Moto , near Mutsora , a station in the Virunga National Park , formerly the Albert National Park, western foothills of the Rwenzori Mountains (0.3166667°N, 29.75°E), 1100 – 1200 m asl, in the intermediate/transitional forest zone GoogleMaps . The Rwenzori Mountains lie on the border between Uganda and the DRC and reach 5109 m asl, which is high enough to support permanent snowcaps and glaciers despite its close proximity to the equator ( Plumptre et al. 2007) . This mountain range is one of the sources of the Nile River and includes two national parks: the Rwenzori Mountains National Park and the Virunga National Park .

Ecology

The Rwenzori Mountains lie in the DRC and Uganda in the southern part of Upper Nile Ecoregion 522 ( Thieme et al. 2005; Abell et al. 2008) which includes Lake Albert and the River Semuliki in the Western Rift Valley. Most of this ecoregion lies to the north of these mountains in the drainage basin of the River Nile in South Sudan, Sudan and Ethiopia, and includes the vast Sudd swamplands. Both of the known localities where P. rwenzori sp. nov. occurs (in the western foothills and in the central and eastern side of the Albertine Rift Valley) are in protected areas (the Rwenzori Mountains National Park and the Virunga National Park). The Rwenzori Mountains National Park is in Kabarole, Kasese and Bundibugyo Districts in Western Uganda and is a UNESCO World Heritage Site that borders the Virunga National Park in the DRC. Despite the apparent protection offered by these two national parks there are potential threats from agricultural encroachment and collection of wood in the parks, with the result that the Rwenzori Mountains National Park is also on the List of World Heritage in Danger ( Plumptre et al. 2007).

Conservation status

An IUCN conservation assessment of P. rwenzori sp. nov. has not yet been carried out, but given the fact that this species is known from only a few specimens from two localities it will

probably be eventually regarded as Data Deficient. Each of the localities where this species is known to occur is in a protected area.

Etymology

The new species is named for the Rwenzori Mountains where this species was first collected. The specific epithet rwenzori is used as a Latin noun in apposition. The vernacular name is the Rwenzori crab.

Remarks

Potamonautes rwenzori sp. nov. differs from P. bwindi sp. nov. and P. kivu sp. nov. in that the major cheliped propodus has large teeth along the cutting edges in the proximal region ( Figure 5c View Figure 5 ) (vs a cheliped propodus that has medium and small teeth along the cutting edges in P. bwindi sp. nov. and P. kivu sp. nov.; Figure 5a,b View Figure 5 ); and the tip of the G1 terminal article is straight or only slightly upturned ( Figure 6c,f) (vs a sharply upturned terminal article tip in P. bwindi sp. nov. and P. kivu sp. nov.; Figure 6a,b,d,e).

Potamonautes rwenzori sp. nov. differs from other, similar small-bodied species of freshwater crabs from Uganda in that s3/s4 is a long, deep sulcus that completely crosses the sternum ( Figure 3b View Figure 3 ) (vs two short shallow sulci at the margins and otherwise smooth in P. elgonensis and P. kanstyore ) ( Cumberlidge and Clark 2010a, 2017); the third maxilliped ischium has a deep vertical sulcus ( Figure 4c View Figure 4 ) (vs a smooth ischium lacking a sulcus in P. amalerensis , P. busungwe , P. elgonensis , P. entebbe , P. imatongensis , P. kantsyore and P. morotoensis ; cf. Cumberlidge and Clark 2010a, 2016, 2017); the cheliped carpus distal tooth is large and pointed ( Figure 5f View Figure 5 ) (vs a small and low cheliped carpus tooth in P. amalerensis , P. elgonensis , P. loveni , P. morotoensis and P. williams ; cf. Cumberlidge and Clark 2010a, 2010b, 2016); and the cheliped dactylus is broad, not highly arched, and encloses a long rectangular interspace ( Figure 5c View Figure 5 ) (vs a highly arched dactylus enclosing a broad oval interspace in P. amalerensis , P. busungwe , P. elgonensis , P. entebbe , P. imatongensis , P. loveni , P. morotoensis , P. mutandensis and P. williamsi ; cf. Cumberlidge and Clark 2010a, 2010b, 2016, 2017; Cumberlidge and Meyer 2011).

Potamonautes rwenzori sp. nov. is also found in the same region of Uganda as P. aloysiisabaudiae and the two species share a number of carapace characters such as an extremely low exorbital tooth, an epibranchial tooth that is reduced to a small granule, and a smooth anterolateral margin immediately behind the epibranchial tooth. The two species can be distinguished in that P. rwenzori sp. nov. is a small species that is adult at CW 24 mm (vs P. aloysiisabaudiae which is adult at CW 45 mm), and the margin of the merus of the cheliped of P. rwenzori sp. nov. is granulated with a small but distinct distal meral tooth ( Figure 5f View Figure 5 ) (vs P. aloysiisabaudiae which has a cheliped merus margin that is smooth with a distal meral tooth reduced to a granule); and the distal tooth of the cheliped carpus is large and pointed ( Figure 5f View Figure 5 ) (vs a low blunt cheliped carpus tooth in P. aloysiisabaudiae ); and the ischium of the third maxilliped is smooth ( Figure 4c View Figure 4 ) (vs an ischium with a distinct vertical groove in P. aloysiisabaudiae ).

General remarks

Potamonautes bwindi sp. nov., P. kivu sp. nov. and P. rwenzori sp. nov. share a number of characters with each other and several additional species in this genus from East Africa. For example, the three new species described here all share an extremely low exorbital tooth and an epibranchial tooth that is reduced to a small granule; all have a smooth anterolateral margin immediately behind the epibranchial tooth ( Figures 1a View Figure 1 , 2a View Figure 2 , 3a View Figure 3 ); and all are adult at a small carapace size (CW 19.8 – 24.0 mm). Ugandan crabs that share this suite of characters include P. amalerensis , P. busungwe , P. elgonensis , P. entebbe , P. imatongensis , P. kantsyore , P. loveni , P. morotoensis , P. mutandensis , P. rukwanzi and P. williamsi (cf. Corace et al. 2001; Cumberlidge and Clark 2010a, 2010b, 2016, 2017; Cumberlidge and Meyer 2011).

Until the present study, only three species of freshwater crabs were known from the Albertine Rift Valley: two large and abundant species of river crabs ( P. aloysiisabaudiae and P. niloticus ), and one small lake-living species ( P. mutandensis ) ( Cumberlidge and Meyer 2011). Potamonautes aloysiisabaudiae is widespread throughout western Uganda and its range includes the Virunga and Rwenzori Mountains and the associated rivers and lakes that flow north into the Nile River basin ( Bott 1955; Cumberlidge unpubl. data). Potamonautes niloticus is one of the most widespread species in Africa and is found throughout the Nile River basin from Rwanda to Egypt ( Cumberlidge 2009), while P. mutandensis occurs in lakes from southern Uganda to Lake Kivu in Rwanda ( Cumberlidge and Meyer 2011).