Potamonautes imatongensis, Cumberlidge & Clark, 2016

Cumberlidge, Neil & Clark, Paul F., 2016, Two new species of freshwater crabs from the highlands of northern Uganda, East Africa and a redescription of Potamonautes amalerensis (Rathbun, 1935) stat. rev. from Mount Kadam (Brachyura: Potamoidea: Potamonautidae), European Journal of Taxonomy 182 (182), pp. 1-18 : 3-9

Potamonautes imatongensis sp. nov.

urn:lsid:zoobank.org:act:3FEF2D5C-9660-4C99-AC96-E9DEE74E1412

Figs 1 A–B; 2A–B, G, J; 3A–B, G–H; 4 A–C; 7A–B; 8

Diagnosis

Postfrontal crest faint but complete, lateral ends well defined, meeting epibranchial teeth; exorbital tooth low, blunt; epibranchial tooth reduced to granule; anterolateral margin posterior to epibranchial tooth smooth. Third maxilliped ischium lacking vertical groove. Sternal sulcus s3/s4 deep at edges, faint medially, almost meeting thickened, raised anterior margin of sternoabdominal cavity; margins of s4 distinctly raised, thickened. Fixed finger (propodus), movable finger (dactylus) of major cheliped of adult male both slim, elongated, lined by small teeth; movable finger (dactylus) highly arched, enclosing oval interspace when closed. Cheliped carpus: first tooth medium sized, pointed; second tooth small, broad, pointed. G1 terminal article short, straight, in line with longitudinal axis, cone-shaped, evenly tapering, tip narrow, tube-like.

Etymology

The new species is named for the Imatong Mountains on the border between Uganda and South Sudan, which is the locality where this species was first collected.

Material examined

Holotype

UGANDA: adult Ƌ, CW 21.5, CL 14.4, CH 7.4, FW 6.5 mm, Imatong Mountains , near border with South Sudan (3.79° N, 32.87° E), at 2,134 m asl, 11 Aug. 1955, L.C. Beadle ( NHM 1955.11.8.26–27).

Paratypes

UGANDA: 5 adult ƋƋ, CWs 19.7, 18.7, 21.5, 18.6, 18.2; 2 adult ♀♀, CWs 20.5, 21.3 mm, Aringa River, northern Acholi District (3.74° N, 32.90° E), at 1,173 m asl, 11 Aug. 1955, L. C. Beadle ( NHM 1955.11.8.20–25).

Other material examined

UGANDA: adult Ƌ, CW 21.5, CL 14.7, CH 7.7, FW 6.5 mm ( NHM 2016.16); 5 adult ƋƋ, CWs 20.0, 18.0, 19.2, 21.2, 21.3 ( NHMUK 2016.17-21); 4 adult ♀♀, CWs 23.1, 19.4, 18.2, 19.2 mm ( NHMUK 2016.22-25), 2 juveniles CW 12.1, 13.0 mm ( NHMUK 2016. 26-27), tributary of the Aringa River at Lututuru (48 km north of Kitgum), Imatong Mountains, northern Acholi District near border with South Sudan (3.75° N, 32.90° E), at 1,524 m asl, 22.5 °C, at 4:00 pm, 16 May 1968, A.W.R. McRae ( NMU TRW 1968.03); adult Ƌ, CW 21.5, CL 14.4, CH 7.4, FW 6.5 mm, Aringa River, northern Acholi District (3.74° N, 32.90° E), 1,173 m asl, 11 Aug. 1955, L. C. Beadle ( NHM 1955.11.8.20–25).

Type locality

Uganda, Imatong Mountains, near border with South Sudan (3.79° N, 32.87° E), at an altitude of 2,134 m asl.

Description

Based on holotype (adult male CW 21.5). Carapace outline transversely oval, medium height ( CH /FW 1.1); front broad, measuring one-third CW (FW/CW 0.30). Postfrontal crest faint but complete, lateral ends well defined, meeting epibranchial teeth; epigastric crests clear, median sulcus between crests short, forked posteriorly, semi-circular, urogastric, cardiac, posterior, cervical carapace grooves all distinct. Exorbital tooth low, blunt; epibranchial tooth reduced to granule; anterolateral margin posterior to epibranchial tooth smooth; anterolateral margin between exorbital, epibranchial teeth smooth, curving slightly outward, lacking intermediate tooth; carapace sidewall vertical sulcus faint, incomplete, 5.5 mm; G = 4.6 mm; H = 4.9 mm; I = 7.8 mm; J = 5.9 mm; K = 7.3 mm; L = 9.5 mm.

not meeting anterolateral margin. Suborbital margin smooth. Carapace sidewall pterygostomial region with distinct granulated vertical sulcus, ending at longitudinal sulcus, dividing sidewall into 3 parts. Third maxilliped exopod with long flagellum, ischium lacking vertical groove. Epistomial tooth large, triangular, edges lined by large rounded granules. Mandibular palp 2-segmented; terminal segment simple. Thoracic sternal sulcus s2/s3 deep, running horizontally across sternum; thoracic sternal sulcus s3/s4 deep at edges, faint medially, almost meeting thickened, raised anterior margin of sternoabdominal cavity; margins of s4 distinctly raised, thickened. Thoracic episternal sulci s4/e4, s5/e5, s6/e6, s7/e7 all visible grooves. Chelipeds of adult male unequal; fixed (propodus) and movable (dactylus) fingers of adult male slim, elongated, both lined by small teeth, movable finger (dactylus) highly arched, enclosing oval interspace when closed. Cheliped carpus: first tooth medium size, pointed, second tooth small, broad, pointed. Inferior margins of merus of cheliped with series of small sharp teeth; distal meral tooth pointed; superior surface of merus granulated. Abdomen outline broadly triangular with straight edges. G1 terminal article short, straight, in line with longitudinal axis of gonopod, cone-shaped, evenly tapering, tip narrow, tube-like. G2 terminal article long, flagellum-like.

Size

Small species, adult size range CW 18.2–23 mm.

Colour

Preserved specimens uniformly light brown.

Distribution

The localities where this species is known to occur are in the Aringa River or its tributaries in northern Acholi Province of Uganda close to the border with South Sudan. The Aringa River is part of the Nile River drainage and flows north out of Uganda, eventually meeting the White Nile River in South Sudan (Fig. 10). The third locality from the ‘ Sudan (now South Sudan)/ Uganda border at 7,000 feet (= 2,134 m asl)’ is vague, but has been estimated here based possible places at that altitude in the Aringa River basin in the Imatong Mountains.

Ecology

This species is so far known only from high altitude localities, and has been collected from streams at over 1,500 m asl, and in the Aringa River at 2,134 m asl.

Vernacular name

The Imatong Mountains Crab.

Conservation status

An IUCN conservation assessment of Potamonautes imatongensis sp. nov. has not yet been carried out.

Remarks

Potamonautes imatongensis sp. nov. is superficially similar to several other Potamonautes species that share the following characters: a small body size at maturity (beginning at CW 18 mm), a complete postfrontal crest; completely reduced or absent exorbital and epibranchial teeth; smooth anterolateral margins immediately behind each epibranchial tooth; a third maxilliped ischium that lacks a visible sulcus; the first tooth on the carpus of the cheliped that is strong and pointed; a distal meral tooth of the cheliped that is strong and pointed; and a slim, elongated, highly arched dactylus of the male major cheliped. East African crabs that share this suite of characters include P. mutandensis ( Chace, 1942) (southwest Uganda), P. berardi (Audouin, 1826) (Nile River basin), P. williamsi Cumberlidge & Clark, 2010 (Mount Elgon, Uganda), P. amalerensis ( Rathbun, 1935) stat. rev. and P. morotoensis sp. nov.

Potamonautes imatongensis sp. nov. differs from P. mutandensis in that the second tooth on the carpus of the cheliped is weak, low and blunt (vs pointed and as large as the first carpal tooth in P. mutandensis ), the outer margins of sternal segment s4 are distinctly thickened (vs slim and not thickened in P. mutandensis ; see Chace 1942; Cumberlidge & Meyer 2011), and the G1 terminal article of P. imatongensis sp. nov. is straight and cone-shaped and not directed only slightly outward (vs s-shaped, widened medially, and angled outward at a 45° angle to the longitudinal axis of the gonopod in P. mutandensis ).

Potamonautes imatongensis sp. nov. differs from P. berardi in that the G1 terminal article is straight, cone-shaped and not directed outward (vs straight at first, then bent sharply outward at 45° to the longitudinal axis in the mid-section in P. berardi ) and the outer margins of thoracic sternite s4 are distinctly thickened (vs slender and not thickened in P. berardi ; see Chace 1942; Cumberlidge & Meyer 2011).

Potamonautes imatongensis sp. nov. differs from P. williamsi from Mount Elgon, Uganda, in that the first tooth on the carpus of the cheliped is strong and pointed (vs small and low in P. williamsi ), thoracic sternal sulcus s3/s4 is deep at the edges and medially faint (vs s3/s4 is reduced to two short notches on the external margins of the sternite in P. williamsi ) and the outer margins of thoracic sternite s4 are distinctly thickened (vs slender and not thickened in P. williamsi ; see Cumberlidge & Clark 2010).

As for the species described here, P. imatongensis sp. nov. differs from P. morotoensis sp. nov. in that the G1 terminal article is straight, cone-shaped and tapering, with a long tube-like tip (vs straight at first, bent outward at 45° to the longitudinal axis, and cone-shaped, tapering evenly to a down-turned tip in P. morotoensis sp. nov.), the first tooth on the carpus of the cheliped is medium sized and pointed, and the second carpal tooth is small, broad and pointed (vs both teeth small and low in P. morotoensis sp. nov.) and the dactylus of the cheliped is highly arched, enclosing a widely oval interspace when closed (vs a cheliped dactylus that is only slightly arched and enclosing a long narrow interspace when closed in P. morotoensis sp. nov.).

Potamonautes imatongensis sp. nov. differs from P. amalerensis stat. rev. in that the G1 terminal article is straight and cone-shaped with a long tube-like tip (vs straight at first, bent outward at 45° to the longitudinal axis and cone-shaped, tapering evenly to a pointed tip in P. amalerensis stat. rev.), the first tooth on the carpus of the cheliped is medium sized and pointed, and the second carpal tooth is small, broad and pointed (vs a small first carpal tooth and reduced granule-sized second carpal tooth in P. amalerensis stat. rev.), and the dactylus of the cheliped is highly arched, enclosing a widely oval interspace when closed (vs a cheliped dactylus that is only slightly arched and encloses a long narrow interspace when closed in P. amalerensis stat. rev.).

Figures

Fig. 1. A–B. Potamonautes imatongensis sp. nov., holotype, adult Ƌ, CW 21.5 mm, from the Imatong Mountains in northern Uganda (NHM 1955.11.8.26-27). A. Carapace, dorsal view. B. Carapace, frontal view. — C–D. Potamonautes morotoensis sp. nov., holotype, adult Ƌ, CW 26 mm, from Mount Moroto in northern Uganda (NHM 2015.3056). C. Carapace, dorsal view. D. Carapace, frontal view. — E–F. Potamonautes amalerensis (Rathbun, 1935) stat. rev., holotype, adult Ƌ, CW 31.5 mm, from Mount Kadam, northern Uganda (MCZ 8238). E. Carapace, dorsal view. F. Carapace, frontal view. Scale bar: A–B = 6.3 mm; C–D = 7.3 mm; E–F = 9.1 mm.