Potamonautes congoensis ( Rathbun, 1921 )

Cumberlidge, Neil, 2015, Redescriptions of three species of freshwater crabs from the Democratic Republic of Congo, Central Africa (Brachyura: Potamoidea: Potamonautidae), Zootaxa 3973 (1), pp. 119-138 : 131-136

Potamonautes congoensis ( Rathbun, 1921)

Congo Freshwater Crab

( Figs. 9–12 )

Potamon (Geothelphusa) congoensis Rathbun, 1921: 422 , fig. 11, plate 28, fig. 3; fig. 29.

Potamon (Geotelphusa) congoensis— Parisi 1925: 97.

Geothelphusa congoensis— Balss 1936: 192, fig. 27.

Potamon (Geothelphusa) congoensis— Paris 1925: 97 –98.

Geothelphusa congoensis— Balss 1936: 192 –193, fig. 27.

Potamon congoensis— Chace 1942: 209.

Potamonautes congoensis— Ng et al. 2008: 171; Cumberlidge et al. 2009: appendix item 942.

Type material examined. D.R. CONGO: Orientale Province, Nepoko River at Bafwabaka near Gamangui (2.17° N, 27.33° E) Ituri Forest, adult male holotype (CW 44, CL 29), 1 Feb. 1910 (J. Chapin and H. Lang) ( AMNH 3354). Other material. D.R. CONGO: Poko, Lower Uele (3.15° N, 26.88° E), 4 males, 8 females (one with newly hatched young), 1 juvenile, paratypes ( AMNH 3374); affluent of the Tshopo River, near Kisangani (0.56° N, 25.11° E), 1 female, paratype (J. Chapin and H. Lang) ( AMNH 3402); Bafwabaka (2.11° N, 27.54° E), 1 male, paratype, 31 Dec. 1909 (J. Chapin and H. Lang) ( AMNH 3431); Bafwabaka, 1 male, 1 female, paratypes, 31 Dec. 1909 (J. Chapin and H. Lang) ( AMNH 3439); Bafwasende (1.01° N, 27.16° E), 1 male, paratype, 28 Sep. 1909 (J. Chapin and H. Lang) ( AMNH 3450).

Diagnosis. Postfrontal crest complete, exorbital tooth small, low; epibranchial tooth not visible; anterolateral margin smooth posterior to epibranchial tooth (Fig. 59B); ischium of third maxilliped with deep vertical sulcus ( Fig. 9 J); thoracic sternal sulcus s3/s4 deep at sides, absent in middle ( Fig. 9 C); first carpal tooth on inner margin of carpus of cheliped medium-size, pointed, second carpal tooth small, broad, followed by low tooth ( Fig. 9 F,G); G1 terminal article widened basally then directed strongly outward at a 45° angle, tapering to short, slender up-curved tip ( Fig. 10 A,B).

Redescription. Carapace texture smooth, postfrontal crest complete, epigastric lobes continuous with postorbital crests, lateral ends of postorbital crests meeting anterolateral margins; median sulcus between epigastric crests short, forked posteriorly ( Fig. 9 B). Exorbital tooth small, low; epibranchial tooth not visible; anterolateral margin between exorbital, epibranchial teeth short, smooth, lacking intermediate tooth; anterolateral margin smooth posterior to epibranchial tooth ( Fig. 9 B). Suborbital margin smooth ( Fig. 9 A). Carapace medium height ( CH /FW 1.25); front narrow, measuring almost one-quarter width of carapace (FW/CW 0.26) ( Fig. 9 A). Cervical carapace grooves faint, semi-circular, urogastric, cardiac, posterior carapace grooves all distinct ( Fig. 9 B). Sidewall of carapace with distinct vertical sulcus, ending at longitudinal sulcus, dividing sidewall into three parts ( Fig. 9 A). Exopod of third maxilliped with long flagellum, ischium of third maxilliped with deep sulcus ( Fig. 9 J). Epistomial tooth large triangular. Mandibular palp two-segmented, terminal segment simple ( Fig. 11 F, G). Thoracic sternal sulcus s2/s3 complete running horizontally across sternum; s3/s4 deep at sides, faint or absent in middle ( Fig. 9 C). Thoracic episternal sulci s4/e4, s5/e5, s6/e6, and s7/e7 all deep ( Fig. 9 C). Chelipeds of adult male unequal ( Fig. 9 D, E). Propodus of major (left) cheliped of adult male with swollen palm 1.5 times as long as high, lower margin convex, immovable finger slim; dactylus (moveable finger) of major cheliped long, widened, curved, enclosing wide oval space when closed; teeth irregular, all small; dactylus of minor cheliped long, slender, not arched, fingers almost meeting ( Fig. 9 D,E). First carpal tooth of inner margin of carpus of cheliped slender, pointed, second carpal tooth small, broad, followed by low tooth ( Fig. 9 F, G). Lateral, medial inferior margins of merus of cheliped faintly granular; distal meral tooth reduced to granule; superior surface of merus smooth ( Fig. 9 F, G). Walking legs (p2—p5) moderate length, slender; merus of p2 3.4 times as long as wide; merus of p5 3 times as long as wide ( Fig. 10 A, B). Abdomen outline broadly triangular with straight edges; telson (a7) as long as a6, a7 subtriangular, broader than long, margins slightly sinuous, tip rounded ( Fig. 9 I). G1 terminal article widened basally then directed strongly outward at a 45° angle, tapering to short, slender up-curved tip; G1 terminal article about one-third as long as subterminal segment, longitudinal groove visible on dorsal, superior, ventral sides ( Fig. 10 A,B,C). Broad dorsal membrane on dorsal face of G1 between terminal article and subterminal segment ( Fig. 10 B). G2 terminal article long, flagellum-like ( Fig. 10 D).

Size. Medium-size species, adult starting at CW 44 mm. Hatchlings on mother’s abdomen CW 2.9, CL 2.7.

Color. Dorsal carapace dark glossy black/purple, eyestalks with orange tint, mouthparts gray/blue, thoracic sternum pale gray/yellow, abdomen blue/white, chelipeds pale black/purple, walking legs mottled grey/yellow.

Type locality. Nepoko River at Bafwabaka near Gamangui (Ituri Forest), Orientale Province, D.R. Congo. Close to the town of Bomili where the Nepoko River joins the Ituri River to form the Aruwimi River that flows through the Okapi Wildlife Reserve.

Conservation status. Potamonautes congoensis was listed as Least Concern ( IUCN 2003; Cumberlidge et al.

2009) because it is known from 13 localities and occupies a wide distributional range of over 150,000 km 2. There is no evidence of a decline in the extent and quality of its habitat and there are no long-term threats to its habitat from disturbance and pollution ( Cumberlidge 2008c).

Distribution. This species is found in the tributaries of the Upper Congo River at Kisangani and northeast to the upper Uele River basin of the D.R. Congo close to the border with South Sudan and Uganda ( Fig. 12 ). The species is found at Bafwabaka, Bafwasende, and Kisangani in the Orientale Province of the D.R. Congo in tributaries of the Tshopo River that flows into the Congo River ( Fig. 12 ). Potamonautes congoensis is also know from the following localities in the D.R. Congo: Tshopo Province, Boulevard Lumumba, Kisangani (0.52° N, 25.18° E) (MRAC 24.031); Medje (2.42° N, 27.30° E); MRAC 1.280, Ituri (1.85° N, 29.97° E) (MRAC 1.324); Manda (Mandai) N25 (2.37° N, 27.93° E) (MRAC 1.351); Beni, Kivu-Nord Province (0.48° N, 29.47° E) (MRAC 1.549); Banalia (1.55° N, 25.33° E) (MRAC 0.074); Kibali, Ituri, Orientale Province (2.37° N, 27.93° E) (MRAC 0.100); Arebi (2.81° N, 29.56° E) (MRAC 0.235-0.238); Wamba, Congo-Kinshasa, Orientale Province (2.14° N, 27.99° E) (MRAC 0.299); Poko, Bas Uélé Province (3.15° N, 26.88° E) (MRAC 1.019); and Aba (3.87° N, 30.23° E) (MRAC 1.252). The identity of specimens (4 m, 2 juveniles) collected by J. P. Chapin in Feb 1916 (AMNH 4518) from Gabon (listed as belonging to this species by Rathbun 1921) as “ French Congo: Libreville, Gaboon ” is doubtful because the descriptions and illustrations of these specimens indicate that they may not prove to belong to this species. These specimens have not been included in this revision of P. congoensis .

Habitat. This species was first captured in traditional fish-traps set in heavily forested affluents of the Bomokandi River at Poko that were baited with decomposed manioc (to attract crabs and fishes such as silurids).

Remarks. This redescription is necessary because Bott’s (1955) classification erroneously treated P. congoensis as a junior synonym of P. (Lobopotamonautes) aloysiisabaudinae (Nobili, 1906) from western Uganda. Bott (1955) also treated Potamon (Geothelphusa) antheus Colosi, 1920 , from Ethiopia as a junior synonym of P. (L.) aloysiisabaudiae . Bott (1955) nevertheless reached this conclusion without reference to the type material of P. congoensis or P. antheus . For this reason the present work is based on the examination of the holotype of P. congoensis and of all other relevant taxa. Subsequent authors ( Cumberlidge 1997, 1998; Ng et al. 2008; Cumberlidge et al. 2009), including the present study, did not follow Bott’s (1955) opinions and treated P. aloysiisabaudiae , P. congoensis , and P. antheus as valid species ( Reed & Cumberlidge 2006; Cumberlidge et al. 2009; Cumberlidge & Clark 2012).

Comparisons. Potamonautes congoensis is abundant from the upper reaches of the Congo and Uele Rivers in the forested region northeast of Kisangani in D.R. Congo ( Fig. 12 ). Potamonautes congoensis can be recognized by the characters listed in the diagnosis. Illustrations and photographs of the holotype of P. congoensis were also provided by Rathbun (1921: 422, fig. 11, plate 28, fig. 3; fig. 29) as Potamon (Geothelphusa) congoensis . Potamonautes congoensis is superficially similar to two other species of Potamonautes that occur in the Congo River basin in Central Africa whose exorbital and epibranchial teeth are reduced to granules, and whose anterolateral carapace margins are smooth ( Bott 1955; Cumberlidge 2009). These similar species are P. e m i n i (Hilgendorf, 1892), from northwestern Tanzania and western Uganda ( Reed & Cumberlidge 2006) and P. perparvus ( Rathbun, 1921) from eastern D.R. Congo and Rwanda ( Meyer & Cumberlidge 2011).

Potamonautes congoensis is similar to P. emini in that both species possess a distinct postfrontal crest that completely crosses the carapace, smooth (untoothed) anterolateral margins; a sternal sulcus s3/s4 that is deep at the sides and absent in the middle; a deep vertical sulcus on the third maxilliped ischium; a first carpal tooth of the cheliped that is a large spine; and a second carpal tooth that is small with another small tooth behind it. These two species can nevertheless be distinguished by carapace and G1 characters. For example, P. congoensis is a mediumsize species, adult from CW 44 mm, whereas P. em i n i is a small-size species, adult from CW 36.5 mm. Furthermore, the basal half of the G1 terminal article of P. congoensis is widened ( Fig. 11 A, B), whereas the basal half of the G1 terminal article of P. emini is slim and is not significantly widened ( Reed & Cumberlidge 2006).

Potamonautes congoensis is similar to P. perparvus in that both species possess smooth, untoothed anterolateral margins, a deep vertical sulcus on the third maxilliped ischium, a first carpal tooth of the cheliped that is a large spine, and a second carpal tooth that is small with another small tooth behind it. These two species can nevertheless be distinguished by carapace and G1 characters. Potamonautes congoensis has a distinct postfrontal crest that completely crosses the carapace ( Fig. 9 B), whereas the postfrontal crest is faint and weak in P. perparvus , and the sternal sulcus s3/s4 is deep at the sides and absent in the middle in P. congoensis ( Fig. 9 C), but is deep throughout and completely crosses the sternum in P. perparvus ( Meyer & Cumberlidge 2011) .

Figures

FIGURE 9. Potamonautes congoensis (Rathbun, 1921). Holotype, adult male, CW 44 mm, from the Nepoko River near Kisangani, D. R. Congo (AMNH 3354). A, carapace, frontal view; B, dorsal view; C, anterior thoracic sternum; D, right cheliped, frontal view; E, left cheliped, frontal view; F, carpus and merus of right cheliped, dorsal view; G, carpus and merus of right cheliped, ventral view; H, pereiopod 3; I, pleon (abdomen); J, third maxilliped, frontal view. Scale bar: 14.2 mm (A – I), 3.5 mm (J).

FIGURE 10. Potamonautes congoensis (Rathbun, 1921). Holotype, adult male, CW 44 mm, from the Nepoko River near Kisangani, D. R. Congo (AMNH 3354). A, G 1 ventral view; B, G 1 dorsal view; C, superior view of terminal article; D, G 2 ventral view; E, mandible frontal view; F, mandibular palp superior view. Scale bar: 4.5 mm (A – D), 2.5 mm (E – F).

FIGURE 11. Potamonautes congoensis (Rathbun, 1921). Holotype, adult male, CW 44 mm, from the Congo River at Kisangani, D. R. Congo (AMNH 3353). Whole animal A, dorsal view; B, ventral view. Scale bar: 20 mm (A – B).

FIGURE 12. Map of the D. R. Congo in Central Africa showing the known localities of P. congoensis (black circles, not shown to scale). See text for exact locality coordinates.