Potamonautes elgonensis, Cumberlidge & Clark, 2010

Cumberlidge, Neil & Clark, Paul F., 2010, Two new species of freshwater crabs from Mount Elgon, East Africa (Brachyura: Potamoidea: Potamonautidae) and a re-diagnosis of Potamonautes niloticus (H. Milne Edwards, 1837) with notes on their natural history and onchocerciasis, Journal of Natural History 44 (29 - 30), pp. 1807-1829 : 1812-1818

Potamonautes elgonensis sp. nov.

( Figures 2–4 )

Potamonautes loveni: Williams 1991: 181–187 (part).

Material examined

Type material. Uganda. Holotype. Adult male (cw 47), stn El.142, Jabtarit River, Kiriki sector, Mt Elgon, 2134 m asl, coll. T. R. Williams, 14 January 1961 ( NHM 2008.1000). Paratypes. Adult male (cw 47.7), five subadult males (cw 39.0–25.8), four subadult females (cw 37.7–28.7), 12 juvs, stns El.140 and El.141, Jabtarit River, Kiriki sector, Mt Elgon, 2073 m asl coll. T. R. Williams, 14 January 1961 ( NHM 2010.6–27); one subadult male (cw 38.5), one subadult female (cw 40.5), small rivers and streams above 1372 m asl, western slopes of Mt Elgon, coll. G. R. Barnley, 1957 ( NMU TRW 1959.04); eight males (cw 31.2–10.6), five females (cw 37.6–15.1), 15 juvs, stn El.18, Lasu River, Malawa sector, Mt Elgon, 1539 m asl, coll. T. R. Williams, 27 December 1960 ( NHM 2008.3172–3181); one male (cw 46.7) River Sume, western slopes of Mt Elgon, 1524 m asl, coll. M. A. Prentice, 12 September 1960, pres. T. R. Williams ( NHM 2008.3259); two males (cw 15.9, 13.5), five females (cw 35.9– 19.5), 19 juvs, stn El.36, Ririma River, Malawa sector, Mt Elgon, 1829 m asl, T. R. Williams, 29 December 1960 ( NHM 2008.3219–3228); stn El.62, four males (cw 38.8–16.7), 12 females (cw 38.8–14.8), 12 juvs, Manafwa River, Malawa sector, Mt Elgon, 1402 m asl, coll. T. R. Williams, 1 January 1961 ( NHM 2008.3229–3238); four males (cw 34.1–13.8), nine males (cw 29.7–12.2), seven juvs, stn El.104, Namaugutu River, Namatala sector, Mt Elgon, 1555 m asl, coll. T. R. Williams, 8 January 1961 ( NHM 2008.3312–3312); nine males (cw 45.0–38.00), eight females (cw 29.4–14.1), 10 juvs, stn El.65, Sago-Sago River, Malawa sector, Mt Elgon, 1402 m asl, coll. T. R. Williams, 1 January 1961 ( NHM 2008.3412–3421); one male (cw 29.9), three females (cw 34.4–23.8), stn El.90 Tayaka River, Namatala sector, Mt Elgon, 1463 m asl, from soil among roots at stream edge, coll. T. R. Williams, 7 January 1961 ( NHM 2008.3005– 3008); two males (damaged), two females (cw 47.8, one damaged) stn El.97, Sisiwachi River, Namatala sector, Mt Elgon, 1585 m asl, coll. T. R. Williams, 8 January 1961 ( NHM 2008. 3001–3004); stn El.101, Namatala River, Namatala sector, Mt Elgon, 1463 m asl, coll. T. R. Williams, 8 January 1961 ( NMU TRW 8.I.1961); several males (cw 30.6–14.2), eight females (cw 37.0–16.4), 24 juvs, stn El.102, Namatala River, Namatala sector, Mt Elgon, 1463 m asl, coll. T. R. Williams, 8 January 1961 ( NHM 2008.3422–3431); 10 males (cw 37.0–15.9), nine females (cw 37.2–14.7), nine juvs, stn El.145, north Sirokomu River, Kiriki sector, Mt Elgon, 2134 m asl, coll. T. R. Williams, 14 January 1961 ( NHM 2008.3432–3441); three males (cw 27–10.40, six females (cw 20.9–11.2), seven juvs, stn El.171, Atar River, Nyenye sector, Mt Elgon, 1829 m asl, coll. T. R. Williams, 16 January 61 ( NHM 2008.3239–3248); five males (cw 35.4–12.5), one female (cw 29.2), six juvs, stn El.172, Kyeseberi River, Nyenye sector, Mt Elgon, 1829 m asl, coll. T. R. Williams, 16 January 1961 ( NHM 2008. 3249–3258); one subadult male (cw 20.5), two subadults /juvs (cw 16.0, 16.5), stn El. 29, Namikoma River, Malawa sector, Mt Elgon, 1372 m asl, with P. niloticus , coll. T. R. Williams 28 December 1960 ( NMU El. 29); juv. males (cw 21.5), stn El.179, Sipi stream, Nyenye sector, Mt Elgon, 1463 m asl, bearing Simulium neavei , coll. T. R. Williams, 17 January 1961 ( NMU El.179); two juvs (cw 24.5, 26.0) Sipi Falls, Sipi River, Nyenye sector, Mt Elgon, coll. T. R. Williams ( NMU TRW 1961.02); one subadult male (cw 28.5) one subadult female (cw 27.5) coll. Dr. Buttner, 20 July 1969 ( NMU 20 July 1969); two adult ovig. females (cw 44.5, 43.0), one subadult female (cw 34.5), seven juv. males (cw 37.5–20.5) western slopes Mt Elgon, rivers and streams above 1524 m asl, coll. M. A. Prentice (0°11′0″ N, 30°14′0″ E, DD 0.18, 30.23) ( NMU TRW 1960.08); adult male (cw 49.5) western slopes of Mt Elgon, small rivers and streams above 1372 m asl, coll. G. R. Barnley, 1957 (3°0′0″ N, 34°0′0″ E, DD 3, 34) ( NMU TRW 1959.04); eight males (cw 46.8–32.5), eight females (cw 50.2–37.3), River Sume, western slopes of Mt Elgon, 1524 m asl, coll. M. A. Prentice, 12 September 1960, pres T. R. Williams ( NHM 2008.3260–3269); adult male, (cw 44.8), three subadult males (cw 36.7, 35.3, 27.9) stream, western side Mt Elgon, coll. P. Hainsworth and P.S. Corbet, February 1956 ( NHM 2010.34–37).

Diagnosis

Based on holotype. Postfrontal crest complete, distinct; epigastric, postorbital crests joining with each other; postorbital crests extending laterally to meet anterolateral margins; exorbital, epibranchial teeth both missing; anterolateral margin immediately behind epibranchial tooth completely smooth; ischium of third maxilliped either smooth or with faint vertical suture; thoracic sternal suture s3/s4 reduced to two faint short side notches; dactylus of major cheliped slightly arched enclosing long narrow interspace when closed; first, second carpal teeth on carpus of cheliped weak, low, blunt; ventral margins of merus of pereiopod 1 both weakly granulated; distal meral tooth either low or missing; terminal article of GO1 curved outward, broadened medially; dorsal membrane broad. Large species, adult size range beginning cw 45 mm, largest specimen cw 50 mm.

Description

Carapace ovoid, wide (cw/fw 3.15), medium high (ch/fw 1.2); surface completely smooth semi-circular, urogastric, transverse branchial grooves present. Front straight, relatively narrow, about one-third carapace width (fw/cw 0.32), anterior margin sharply deflexed. Postfrontal crest distinct. Anterolateral margin between exorbital, epibranchial teeth smooth, lacking intermediate tooth; exorbital, epibranchial teeth reduced to small granules, anterolateral margin completely smooth, continuous with posterolateral margin. Suborbital margin raised, completely smooth. Suborbital, subhepatic, pterygostomial carapace regions all completely smooth; sidewall divided into three parts by longitudinal (epimeral) suture (dividing suborbital, subhepatic regions from pterygostomial region), and by vertical (pleural) groove (dividing suborbital from subhepatic regions), dorsal end of vertical groove meeting epibranchial tooth. First thoracic sternal suture s1/s2 deep; second suture s2/s3 deep, running horizontally across sternum; third suture s3/s4 missing except for two faint notches on sides; episternal sulci s4/e4, s7/e7 absent, s5/e5, s6/e6, complete. Third maxillipeds filling entire oral field, except for transversely oval respiratory openings at superior lateral corners; long flagellum on exopod of third maxilliped, ischium of third maxilliped either smooth or with very faint vertical suture. Epistomial tooth prominent, smooth, triangular. Mandibular palp two-segmented; terminal segment single, undivided, with setae (but no hard flap) at junction between segments. Dactylus of adult male major cheliped thickened, slightly arched, enclosing long narrow interspace when closed. First carpal tooth of cheliped weak, low, blunt; second carpal tooth smaller, also weak, low, blunt, followed by several small granules; ventral margins of merus of pereiopod 1 both weakly granulated; distal meral tooth either low or missing; superior surface of merus smooth. Pereiopods p2–p5 slender, p3 longest, p5 shortest, dactyli of p2–p5 tapering to point, each bearing four rows of downward-pointing short, sharp spines. Adult male abdomen triangular, somites a1–a6 of male abdomen four-sided, telson (a7) a triangle with rounded apex; somites a5–a6 broadest. Terminal article of GO1 curving outward, widened medially in the middle; broad dorsal membrane; margins of subterminal segment of GO1 setose.

Distribution

Potamonautes elgonensis is known only from the western and northern slopes of Mt Elgon in Uganda at medium altitudes between 1402 and 2134 m asl in five river drainage sectors: Malawa, Manafwa and Namatala (west), and Kiriki and Nyenye (north) ( Williams 1991) .

Comparisons

Williams (1991) considered the first gonopod characters of P. elgonensis and P. loveni to be identical, and treated these taxa as a single species ( P. loveni ), interpreting differences in the degree of expression of the postfrontal crest, and in species size and colour to be the result of intraspecific character variability. The present study indicates that the material used in the redescription of P. loveni by Williams (1991) actually comprised specimens that belonged to two different species; P. loveni ( Colosi, 1924) (re-described by Cumberlidge and Clark 2009), and P. elgonensis sp. nov. For example, the first gonopod characters of adult male specimens of P. loveni and P. elgonensis , although similar, are not identical, i.e. the terminal article of P. loveni is almost straight and slim, whereas that of P. elgonensis is curved distinctly outward and widened medially in the middle. In addition, P. loveni is a smaller species, with an adult size range between cw 35 mm and cw 49 mm (while the adult size range of P. elgonensis is between cw 45 mm and cw 50 mm); the postfrontal crest is faint or missing in P. loveni (it is distinct in P. elgonensis ), and the carapace of P. loveni is a darker colour than that of P. elgonensis (which is pale). Finally, the dactylus of the major cheliped of adult male of P. loveni is highly arched, encloses an oval interspace when closed, and lacks dentition (whereas the dactylus of adult males of P. elgonensis is widened but only slightly arched, encloses a long rectangular interspace when closed, and has several large rounded teeth).

Specimens of P. elgonensis are known only from the western and northern (Ugandan) side of Mt Elgon (in the Malawa, Manafwa, Namatala, Kiriki and Nyenye drainage sectors) where their distribution overlaps with that of P. loveni . In contrast, Mt Elgon represents the western limit of the range of P. loveni ; this species is also found in the eastern and southern (Kenyan) sides of Mt Elgon (in the Suam and Nzoia drainage sectors) and from the Cherangani Hills to the Mau Range, including the Kakamega Forest and the Nandi Hills, as far east as Lake Naivasha in the Rift Valley ( Cumberlidge and Clark 2009).

Remarks

The taxonomic confusion surrounding the identities of the freshwater crabs from western Kenya arises from a number of sources, including long-standing opinions on species synonymies, some that have proved to be in error ( Bott 1955), the confusion of two different species ( Williams 1991), and the lack of understanding of the morphological changes that accompany growth in these species ( Reed and Cumberlidge 2006; Cumberlidge and Clark 2009).

Etymology

The species is named in recognition of its known distributional range that indicates that it is restricted to the western and northern slopes of Mt Elgon in Uganda.

Figures

Figure 2. Potamonautes elgonensis sp. nov. Male, paratype, cw 49.5, from Mount Elgon, Uganda (NMU TRW 1959.04). (A) Cephalothorax, frontal view; (B) carapace, dorsal view; (C) cheliped, left (minor) frontal view; (D) cheliped, right (major) frontal view; (E) carpus and merus of right cheliped, dorsal view; (F) carpus and merus of right cheliped, inferior view; (G) abdomen. Scale bar represents 12.4 mm.

Figure 3. Potamonautes elgonensis sp. nov. Adult male, paratype, cw 49.5 mm, from Mount Elgon, Uganda (NMU TRW 1959.04). (A) Left third maxilliped; (B) anterior sternum; (C) left first gonopod ventral view; (D) left first gonopod dorsal view. Scale bar represents 12.4 mm (A,B) or 4.5 mm (C,D).

Figure 4. Potamonautes elgonensis sp. nov. Adult male, paratype, cw 49.5 mm, from Mount Elgon, Uganda (NMU TRW 1959.04). Cheliped: (A) right (major) frontal view; (B) left (minor) frontal view; whole animal: (C) dorsal view; (D) ventral view; (E) carapace, frontal view. Photograph Phil Crabb, NHM Photographic Unit.