Potamonautes morotoensis, 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 : 9-17

Potamonautes morotoensis sp. nov.

urn:lsid:zoobank.org:act:C751A933-6705-487F-9FEF-4584DC0DA4B7

Figs 1 C–D; 2C–D, H, K; 3C–D, I–J; 5A–C; 7C–D; 8

Diagnosis

Based on holotype (adult male CW 26). Carapace outline transversely oval, medium height ( CH /FW 1.0); exorbital tooth low, blunt, epibranchial tooth reduced to granule, postfrontal crest complete faint medially, lateral ends well defined meeting epibranchial teeth; anterolateral margin posterior to epibranchial tooth smooth; carapace sidewall vertical sulcus meeting anterolateral margin. Third maxilliped ischium lacking vertical groove. Sternal sulcus s3/s4 deep, completely crossing sternum, meeting thickened, raised anterior margin of sternoabdominal cavity; margins of s4 distinctly raised, thickened. Chelipeds of adult male unequal; movable finger (dactylus) and fixed finger (propodus) of major cheliped of adult male slim, elongated, fixed finger (propodus) with 2 large teeth proximally followed by series of small teeth; movable finger (dactylus) slightly arched, enclosing narrow rectangular interspace when closed. Inferior margins of merus of cheliped lined by series of small granules, distal meral tooth small pointed; superior surface of merus granulated. Cheliped carpus first and second teeth small, low, equal-sized. G1 terminal article short, straight, in line with longitudinal axis, cone-shaped, evenly tapering to pointed tip.

Etymology

The new species is named for Mount Moroto in Karamoja District, Uganda which is the only locality where this species has been collected.

Material examined

Holotype

UGANDA: adult Ƌ, CW 26, CL 17, CH 8.4, FW 8.4 mm (photographed), Lipath River , Mt. Moroto , near Matheniko Game Reserve, Karamoja District (2.54° N, 34.73° E), extreme headwaters, about 2,438 m asl, in grassland, 9 Jul. 1963, T.R. Williams ( NHM 2015.3056 , formerly TRW collection 9 Jul.1963).

Type locality

Uganda, Lipath River, Mt. Moroto, near Matheniko Game Reserve, Karamoja District (2.54° N, 34.73° E), extreme headwaters, about 2,438 m asl, in grassland.

Description

Carapace medium height ( CH /FW 1.0); front broad, measuring one-third CW (FW/CW 0.32). Semicircular, urogastric, cardiac, posterior, cervical carapace grooves all distinct. Postfrontal crest complete, faint medially, lateral ends well defined meeting epibranchial teeth; exorbital tooth low, blunt. Epigastric crests clear, median sulcus between crests short, forked posteriorly. Epibranchial tooth reduced to granule; anterolateral margin between exorbital, epibranchial teeth smooth, curving slightly outward, lacking intermediate tooth; anterolateral margin posterior to epibranchial tooth smooth; carapace sidewall vertical sulcus faint, incomplete, not meeting anterolateral margin. Suborbital margin smooth. Carapace sidewall 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 round 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 in middle, 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; movable finger (dactylus) and fixed finger (propodus) of major cheliped of adult male slim, elongated, propodus with 2 large teeth proximally followed by series of small teeth, dactylus slightly arched, enclosing narrow rectangular interspace when closed. Inferior margins of merus of cheliped with series of small granules, distal meral tooth small pointed; superior surface of merus granulated. Cheliped carpus first, second teeth small, low, equal-sized. Abdomen outline broadly triangular with straight edges. G1 terminal article short, straight, in line with longitudinal axis, cone-shaped, evenly tapering to broad tip. G2 terminal article long, flagellum-like.

Size

Small species, adult at CW 26 mm.

Colour

Preserved specimens uniformly light brown.

Distribution

Mount Moroto (2,438 m asl) in Karamoja Province, northern Uganda.

Ecology

This species is so far known only from a single high altitude locality, and was collected from a mountain stream at 2,438 m asl.

Conservation status

An IUCN conservation assessment of Potamonautes morotoensis sp. nov. has not yet been carried out, but given the fact that this species is known from a single specimen from a single locality it would probably be regarded as Data Deficient.

Vernacular name

Mount Moroto Crab

Remarks

Potamonautes morotoensis sp. nov. is superficially similar to several other Potamonautes species that share the following characters: a small body size at maturity, 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; a first tooth on the carpus of the cheliped that is strong and pointed; a strong and pointed distal meral tooth; and a slim, elongated, highly arched dactylus of the cheliped. East African crabs that share these characters include Potamonautes imatongensis sp. nov., P. mutandensis ( Chace, 1942) (southwest Uganda), P. berardi (Audouin, 1826) (Nile River basin), and P. williamsi Cumberlidge & Clark, 2010 (Mount Elgon, Uganda).

Potamonautes morotoensis sp. nov. differs from P. amalerensis stat. rev. in that the second tooth on the carpus of the cheliped is small and low (vs the second carpal tooth is reduced to a granule in P. amalerensis stat. rev.) and the G1 terminal article tapers evenly to a broad tip (vs G1 terminal article tapering evenly to a pointed tip in P. amalerensis stat. rev.).

For comparisons of P. morotoensis sp. nov. with P. imatongensis sp. nov., see above.

Potamonautes amalerensis ( Rathbun, 1935) stat. rev. Figs 1 E–F; 2E–F, I, L, 3E–F, K–L, 6A–C, 7E–F, 8

Potamon (Geothelphusa) amalerensis Rathbun, 1935: 25 , pl. 2.

Potamonautes amalerensis Ng et al., 2008: 170 (in catalogue).

Potamon amalerensis – Chace 1942: 204, fig 8.

Potamonautes amalerensis – Cumberlidge et al. 2009, appendix 1: 894 (in list).

Rediagnosis

Carapace medium height ( CH /FW 1.1); exorbital tooth low, blunt, epibranchial tooth 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; carapace sidewall vertical sulcus meeting anterolateral margin. Third maxilliped ischium lacking vertical groove. Sternal sulcus s3/s4 deep, completely crossing sternum, meeting thickened, raised anterior margin of

C.

Ventral view, anterior sternum. Scale bars: 21.4 mm. sternoabdominal cavity; margins of s4 distinctly raised, thickened. Inferior margins of merus of cheliped with series of small granules, distal meral tooth pointed; first cheliped carpal tooth small, second cheliped carpal tooth reduced to small granule. Fixed finger (propodus) and movable finger (dactylus) of major cheliped of adult male each with larger teeth interspersed with small teeth, dactylus slightly arched,

enclosing long narrow interspace when closed. G1 terminal article short cone-shaped, directed outward at 45° angle to longitudinal axis of gonopod, evenly tapering to pointed tip.

Material examined

Holotype

UGANDA: adult Ƌ, CW 26, CL 17.4, CH 8.4, FW 8.4 mm, Amaler River , Mt. Kadam (formerly Mt. Debasien), Karamoja District (1.72° N, 34.72° E), at 1,524 m asl, Sep. 1933, A. Loveridge ( MCZ 8238 ).

Paratypes

UGANDA: adult 4 ƋƋ, adult 5 ♀♀, 1 juvenile, Amaler River, Mt. Kadam (formerly Mt. Debasien), Karamoja District (1.72° N, 34.72° E), at 1,524 m asl, Sep. 1933, A. Loveridge ( MCZ 8237).

Other material examined

UGANDA: adult Ƌ, CW 31.5 mm, north side of Mt. Kadam (formerly Mt. Debasien), Karamoja District (1.81° N, 34.71° E) ( NMU TRW 1962.04).

Type locality

Uganda, Amaler River, Mt. Kadam (formerly Mt. Debasien), Karamoja District (1.72° N, 34.72° E).

Size

Small species, adult size range between CW 26.0– 31.5 mm.

Colour

Preserved specimens uniformly light brown.

Distribution

Uganda, Amaler River, Mt. Kadam (formerly Mt. Debasien), Karamoja District in Karamoja Province, northern Uganda. This species is known from only two localities: Amaler River (1.72° N, 34.72° E), and the north side of Mt. Kadam (1.81° N, 34.71° E).

Ecology

This species was collected from high altitude mountain streams at 1,524 m asl.

Vernacular name

Mount Kadam Crab.

Conservation status

This species is known only from two localities both on Mount Kadam in Uganda, and from a total of 11 specimens collected in 1935 and 1962. Potamonautes amalerensis stat. rev. was listed as Data Deficient ( IUCN 2003; Cumberlidge et al. 2009) in view of the absence of further information on its extent of occurrence, ecological requirements, population size, population trends, and long-term threats ( Cumberlidge 2008). The addition of a second locality on Mount Kadam would probably not warrant a change in assessment category.

Remarks

The type material was collected during the AMNH 1933–1934 Expedition to the then colonies of Kenya and Uganda led by Mr. Arthur Loveridge, a Fellow of the Guggenheim Memorial Foundation. Potamon (Geothelphusa) amalerensis Rathbun, 1935 stat. rev., is redescribed here as the valid species Potamonautes amalerensis stat. rev., because Bott (1955) erroneously treated this taxon as a junior synonym of Potamonautes (Rotundopotamonautes) didieri (Rathbun, 1904) from the D.R. Congo ( Cumberlidge & Clark 2012). This opinion of Bott (1955) is further undermined by the fact that he re-described P. didieri based on a non-type museum specimen from ‘Ethiopia’ using photographs of the carapace and illustrations of the gonopods of this (unidentified) specimen (ZSM, CW 37 mm). As a result, a number of subsequent authors ( Cumberlidge 1997, 1998; Ng et al. 2008; Cumberlidge et al. 2009) did not accept the opinion of Bott (1955), and recognized P. didieri and P. amalerensis stat. rev. as valid Potamonautes species. Illustrations and photographs of the holotype of P. amalerensis stat. rev. were provided by Rathbun (1935: 25, plate 2) as Potamon (Geothelphusa) amalerensis stat. rev. and by Chace (1942: 204, fig. 8) as Potamon amalerensis stat. rev.

Potamonautes amalerensis stat. rev. is superficially similar to several other species of African freshwater crabs in that they 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; a cheliped merus with a strong and pointed distal meral tooth; and a slim, elongated, arched dactylus of the male major cheliped that when closed encloses either a wide oval interspace or a long narrow interspace. For comparisons of P. amalerensis stat. rev. with P. morotoensis sp. nov. and P. imatongensis sp. nov. see above.

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.