Potamonautes niloticus (H. Milne Edwards, 1837 )

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 : 1808-1812

Potamonautes niloticus (H. Milne Edwards, 1837)

( Figure 1 )

Telpheusa nilotica H. Milne Edwards 1837: 12 .

Thelphusa nilotica: White 1847: 29 ; H. Milne Edwards 1853: 210; A. Milne-Edwards 1854: 170, pl. 12, fig. 2; Herklots, 1861: 13; Hilgendorf 1869: 109; Miers 1886: 214; Bell 1894: 166.

Parathelphusa nilotica: A. Milne-Edwards 1887: 141 ; Hilgendorf 1898: 21, fig. 7; Nobili 1906: 1; 1909: 357.

Potamon (Acanthothelphusa) nilotica: Ortmann 1897: 300 .

Potamon (Parathelphusa) niloticus: Rathbun 1905: 263 , pl. 12, fig. 15; Lenz 1912: 3.

Potamon (Acanthothelphusa) niloticum: Colosi 1919: 52, 1920: 27 .

Potamon (Potamonautes) niloticum: Colosi 1924: 12 , fig. 7.

Potamonautes niloticus: Balss 1929: 348 ; Chace 1942: 218.

Potamon nilotica: Flower 1931: 733 .

Potamon (Acanthothelphusa) niloticus: Rathbun 1933: 258, 1935: 25 .

Potamon niloticus: Capart 1954: 841 , figs 35, 16.

Potamonautes (Acanthothelphusa) niloticus: Bott 1955: 260 , pl. XIII fig. 1a–c, fig. 30a,b; Monod 1980: 382–383, pl. IV, fig. 22.

Potamonautes niloticus: Cumberlidge 1997: 579, 1998: 202 , 2009a: 548–549, 551–557, Fig. 1 ; Ng et al. 2008: 171.

Material examined

Nontype. Uganda. Six males (cw 44.3–12.4), three females (cw 23–12.9), stn El. 34, Kamijaro River , Manafwa sector, Mt Elgon, 1204 m asl, coll. T. R. Williams, 28 December 1960 ( NHM 2008.3143 – 3150 ); six males (cw 37.6–25.1, 1 damaged), three females (cw 30.2–23.2), stn El. 49 , Manafwa River , Manafwa sector, Mt Elgon, 1280 m asl, coll. T. R. Williams, 1 January 1961 ( NHM 2008.3163 – 3171 ); one male (cw 19), three females (cw 28–11.3), stn El 60, Liisi River , Manafwa sector, Mt Elgon, 1219 m asl, coll. T. R. Williams, 1 January 1961 ( NHM 2008.3139 – 3142 ); one male (cw 38), one female (cw 32.2), stn El. 78, Nalakwa River , Manafwa sector, Mt Elgon, 1402 m asl, coll. T. R. Williams, 3 January 1961, with P. loveni ( NHM 2008.3301 – 3302 ); one male (cw 54), stn El. 79, Nalakwa River , Manafwa sector, Mt Elgon, 1402 m asl, coll. T. R. Williams, 3 January 1961 ( NHM 2008 . 3307); eight males (cw 32.2–13.6), two females (cw 30.6, 13.8), stn El 81 Zuzu River , Namaiala sector, Mt Elgon , 1374 m asl, coll. T. R. Williams , 3 January 1961 ( NHM 2008.3151 – 3162 ); two males (cw 49, 40.3), three females (cw 59.2–42.6), stn El 123, Buyi River , Mt Elgon , 1374 m asl, coll. T. R. Williams , 10 January 1961 ( NHM 2008.3322 – 3326 ); two males (cw 38.1, 37.4), stn El 130, Siroko River , Siroko sector, Mt Elgon , 1097 m asl, coll. T. R. Williams , 11 January 1961 ( NHM 2008.3137 – 3138 ); two female adults (cw 58.9, 52.1), three female subadults (cw 27.2–29.9), two juvs (cw 15.7, 15.4), River Somso , Budongo Forest (crabs with Simulium pupae), coll. G. Barnley ( NHM 1955.11.8.30–33); one male (cw 42.1), lakeshore , Jinja, 701 m asl, coll. R. H. Lowe, 1 August 1953, pres. P. S. Corbet, EAFRO ( NHM 2010.30 ) ; one female (cw 39.3), Ripon Falls, Lake Victoria , coll. 3 May 1954, pres. P. S. Corbet, EAFRO ( NHM 2010.32 ) ; one male (cw 54.7), caught in gill nets set between Sagits and Vumba Island, coll. J. Hinchcliffe, 15 February 1956, pres. P. S. Corbet , EAFRO ( NHM 2010.33 ) ; one male (cw 41.0), Rivers Agoye, Nyara, Wariki , Aduka of the Ala River and Ora River drainage systems near Arua, West Nile , coll. P. Hainsworth, July–August 1955 ( NHM 2010.38 ) ; one female (cw 51.1), caught in gill net set in Pilkington Bay, Lake Victoria , coll. J. D. Roberts, 25 February 1955, pres. P. S. Corbet, EAFRO ( NHM 2010.31 ) . Kenya. One male (cw 53.4), stn EA62.141, Sergoi River at Soy (between Eldoret and Kitale) Kakamega to Kitale region (0°35′0″ N, 35°1′0″ E, DD 0.58, 35.02), Western Province , Kenya , 26 March 1961, with Potamonautes loveni ( NHM 2008.3388 ) ; two adult males (cw 67.7, 56.2) two adult females (cw 61.5, 61.3), Yala River, Kaimoisi , 2000 m asl, coll. I. Gordon, 9 June 1964 ( NHM 2010.1 – 4 ) . Egypt. Several subadults and juvs, first cataract of the Nile , Aswan, coll. W. Langmore ( NHM 1892.10.23.1–6); adult female (cw 48.7), Nile near Cairo, coll. S. S. Flower ( NHM 2010.5 ) ; adult female, Nile near Samannud , coll. 14 July 1899 ( NHM 1908.1.9.1); adult ovig. female (cw 48.6), Nile near Cairo, Giza Zoological Museum, Zoological Survey of Egypt , coll. S. S. Flower, 19 January 1922 ( NHM 1922.11.22.12– 17); subadult female (cw 41.7), Nile at Turah near Cairo, Giza Zoological Museum, Zoological Survey of Egypt , coll. C. S. Boyes, 17 February 1919, pres. S. S. Flower, 19 January 1922 ( NHM 1922.11.22.12–17); subadult female (cw 44.9), Nile at Turah near Cairo, Giza Zoological Museum, Zoological Survey of Egypt , coll. C. S. Boyes, 17 February 1919, pres. S. S. Flower, 19 January 1922 ( NHM 1922.11.22.12–17); ovig. female (cw 39.7), Nile near Cairo, Giza Zoological Museum, Zoological Survey of Egypt , coll. S. S. Flower, 19 January 1922 ( NHM 1922.11.22.12–17); female subadult (cw 46), Nile at Turah near Cairo, Giza Zoological Museum, Zoological Survey of Egypt , coll. C. S. Boyes, 17 February 1919, pres. S. S. Flower, 19 January 1922 ( NHM 1922.11.22.12–17) . Israel or Gaza. Subadults, male (cw 21.9), female (cw 18.2), Palestine (exact locality uncertain, may be present day Israel or Gaza), ( NHM 1865.64 ) .

Diagnosis

Based on adult male specimens. Postfrontal crest complete, distinct; epigastric, postorbital crests fused; postorbital crests extending laterally to meet anterolateral margins; exorbital, epibranchial teeth both strong, sharp; anterolateral margin immediately behind epibranchial tooth with row of distinct spines; thoracic sternal suture s3/s4 complete; dactylus of major cheliped strongly arched enclosing broad oval interspace when closed; first carpal tooth on carpus of cheliped strong, pointed, second carpal tooth weak, low, blunt; ventral margins of merus of pereiopod 1 both granulated; distal meral tooth strong, pointed; terminal article of GO1 long, s-shaped, widened in middle, ventral lobe thickened, higher than dorsal lobe, dorsal membrane broad. Large-sized species, adult size range from cw 54 to cw 63 mm.

Distribution

Potamonautes niloticus is a large, conspicuous river crab that has a wide distribution throughout the entire length of the Nile and its tributaries and is known to occur in more than 60 localities in six countries ( Egypt, Sudan, Ethiopia, Uganda, Kenya and Rwanda) and Lake Victoria ( Cumberlidge 2009a). This species is endemic to the Nile River basin and has never been found outside this system in sub-Saharan Africa and there are no records from Tanzania, despite its presence in Lake Victoria, Kenya and Uganda ( Reed and Cumberlidge 2006; Cumberlidge 2009a,b). The records reported in the present study indicate that P. niloticus also occurs in the Mediterranean zoogeographical subregion of the Palaearctic, which is well outside the Afrotropical region. Most of these additional localities are from the Nile River in Lower Egypt from Cairo, Turah and Samannud (which lies on the Damietta branch of the Nile in the central Delta), but one is from “ Palestine ”, which, if confirmed, would further extend the range of this species outside the Afrotropical region. Moreover, all of these specimens were collected between 88 and 140 years ago and the authors are not aware of any new material that has been collected from the freshwater habitats that lie between southern Israel and the Nile Delta.

Ecology

Potamonautes niloticus occurs in a range of aquatic habitats including the major channels of the Nile itself and its lowland tributaries, in small and large lakes associated with the river basin, as well as in small clear fast-flowing mountain streams with rocky beds, and sluggish warm lowland streams with muddy bottoms ( Bott 1955; Williams 1964; Cumberlidge 1997, 1998, 2009a). This species is completely dependent on aquatic habitats and it has never been reported to leave the water whether it is found in streams, rivers or lakes. In the southern parts of its range in Kenya and Uganda, P. niloticus serves as a host for the aquatic larvae of the biting blackfly, Simulium sp. , which are the vectors of Onchocerca volvulus , the parasite that causes river blindness in humans ( Crosskey 1990). There is no evidence that P. niloticus is associated with this disease in the northern part of its range in Egypt and the Sudan.

Conservation status

Potamonautes niloticus is listed ( IUCN 2009) as least concern (LC) in view of its wide distribution, estimated stable population size and abundance (it supports small-scale local fisheries in Lake Victoria in Uganda and Kenya), and the lack of known widespread long-term threats. The stable population estimates are based on the fact that there are large numbers of specimens in museum collections, and on recent collections of this species from Uganda and Kenya, which implies that East African populations are stable, although anecdotal evidence indicates that the populations in Egypt north of the Aswan Dam may well be in decline because the most recent collection date (1922) available is from Lower Egypt (Cumberlidge 2008; Cumberlidge et al. 2009).

Remarks

The type specimen deposited in the Muséum national d’Histoire naturelle, Paris is a dried male, collected from Egypt by Rüppell in 1830 and is in poor condition ( Capart 1954). Consequently the diagnosis given here is based on a non-type adult male specimen collected from the Yala River, Kaimoisi, Kenya (see Figure 1 ) that conforms to the published description of the type. The NHM material from Palestine is worthy of comment because it was initially catalogued as four specimens (one male, three female) of Gecarcinus . All were registered under NHM accession number 1865.64, subsequently re-examined, and identified (by person unknown) as comprising two species. Two adult females (one ovig.) were determined as Thelphusa berardi [now Potamonautes berardi (Audouin, 1826) ], and the others as T. nilotica (now P. niloticus ). Both jars retained the original registration number and the identifications are confirmed here to species level. The record of P. berardi from “ Palestine ”, which was only previously known to occur as far north as Medinet el Fayum on the Nile, suggests that these two species of Potamonautes were sympatric with the potamid Potamon potamios ( Olivier, 1804) which occurs in the eastern Mediterranean region as far south as Israel, Palestine, and El Quseima (Kosseima) in north east Sinai (NHM 1922.11.22.32–33 and NHM 1928.6.7.1–2) in Egypt (Brandis et al. 2000). However, the age of the museum material reported on here means that the distribution status of these three species of freshwater crabs requires updating.

Figures

Figure 1. Potamonautes niloticus (H. Milne Edwards, 1837). Adult male from Yala River, Kenya (NHM 2008.3388). 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.