Potamonautes busungwe, Cumberlidge & Clark, 2017

Cumberlidge, Neil & Clark, Paul F., 2017, Description of three new species of Potamonautes MacLeay, 1838 from the Lake Victoria region in southern Uganda, East Africa (Brachyura: Potamoidea: Potamonautidae), European Journal of Taxonomy 371, pp. 1-19 : 7-9

Potamonautes busungwe sp. nov.

urn:lsid:zoobank.org:act:C6828C1B-D256-4F44-8A89-270F9478CE38 Figs 2 A–B, 4B, 5C–D, 6B, E, 7; Tables 1 , 3 Diagnosis

Based on holotype (adult male CW 15.9 mm). Carapace outline transversely oval, medium height ( CH / FW 1.0); exorbital tooth low, blunt, epibranchial tooth reduced to granule, postfrontal crest complete but faint, lateral ends meeting epibranchial teeth; anterolateral margin posterior to epibranchial tooth smooth ( Fig. 2A ); carapace sidewall vertical sulcus meeting anterolateral margin. Third maxilliped ischium smooth, lacking vertical sulcus; s3/s4 deep at edges, faint in middle; margins of s4 distinctly raised, thickened ( Fig. 2B ). Chelipeds of adult male unequal; movable finger (dactylus) and fixed finger (propodus) of major cheliped of adult male both slim, elongated, both with series of small, even-sized teeth, dactylus highly arched, encompassing wide oval interspace when closed. Inferior margins of merus of cheliped lined by series of small pointed teeth, distal tooth large, pointed; superior surface of merus granulated ( Fig. 2B ). Distal, proximal teeth on inner margin of cheliped carpus small, low, equalsized ( Fig. 2B ). G1 terminal article short (0.25 × length of G1), straight, in line with longitudinal axis of subterminal segment, distal third curving outward, tapering to slightly upcurved tip ( Fig. 6B, E ).

Etymology

The new species is named for the small island of Busungwe in the northwestern part of Lake Victoria near the border with Tanzania, where this species was first collected, and is used as a noun in apposition ( Fig. 7 ). Vernacular name: the Busungwe crab.

Material examined

Holotype (here designated)

UGANDA: adult ♂, CW 15.9, CL 10.6, CH 5.4, FW 5.3 mm, Central Region , Kakuuto , Busungwe Island, - 0.953781° S, 31.783557° E, exposed rocky shore, 21 Apr. 1955, P. Corbett leg., East African Fisheries Research Organization ( NHMUK 2017.37 ).

Paratype (here designated)

UGANDA: adult ovigerous ♀, CW 15.4, CL 10.5, CH 5.3, FW 5.3 mm, Central Region, Kakuuto, Busungwe Island, - 0.950000°S, 31.7833°E, exposed rocky shore, same date and collector as for holotype ( NHMUK 2015.3056).

Description

Carapace of medium height ( CH /FW 1.0; Fig. 2A ), front broad, measuring one-third CW (FW/CW 0.33; Fig. 2B ). Semi-circular, urogastric, cardiac, posterior and cervical carapace grooves all distinct. Postfrontal crest complete, faint, lateral ends meeting epibranchial teeth; epigastric crests faint, median sulcus between crests short, forked posteriorly; exorbital tooth low, blunt; 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 ( Fig. 2A ); carapace sidewall vertical sulcus faint, meeting longitudinal sulcus, dividing sidewall into three parts ( Figs 2B , 4B ). Suborbital margin granulated ( Figs 2B , 4B ). Third maxilliped exopod with long flagellum, ischium smooth, lacking vertical sulcus ( Figs 2B , 4B ). Epistomial tooth large, triangular, edges lined by large round granules. Mandibular palp 2-segmented; terminal segment simple; s2/s3 deep, completely crossing sternum; s3/s4 deep at edges, faint in middle; s4/e4, s5/e5, s6/e6 and s7/e7 all visible ( Fig. 2B ). Chelipeds of adult male unequal; movable finger (dactylus) and fixed finger (propodus) of major cheliped of adult male slim, elongated, with series of small, even-sized teeth, dactylus highly arched, encompassing wide oval interspace when closed ( Fig. 5 C–D). Inferior margins of merus of cheliped lined by series of small pointed teeth, distal tooth large, pointed; superior surface of merus granulated ( Fig. 2B ). Cheliped carpus inner margin teeth both small, low, equal-sized. Pleon outline broadly triangular, with straight edges ( Fig. 2B ). G1 terminal article short (0.25 × length of G1), straight, in line with longitudinal axis of subterminal segment, distal third curving outward, tapering to slightly upcurved tip ( Fig. 6B, E ). G2 terminal article long (0.5 × length of G2), flagellum-like.

SIZE. Small species, adult at CW 15 mm.

COLOUR. Preserved specimens uniformly light brown.

Distribution

Busungwe Island in the northern part of Lake Victoria ( Fig. 7 ). The nearest town on the mainland to Busungwe is Kakuuto, in the Rakai District of the Central Region of southwestern Uganda.

Ecology

Little is known about the ecology of this species. These specimens were collected in 1955 by P. Corbett of the East African Fisheries Research Organization based at Jinja, who sampled offshore islands including Busungwe as part of a study of the fisheries of Lake Victoria. This small island is still relatively undisturbed, with only a few buildings on the northern part of the island.

Conservation status

An IUCN extinction risk assessment of P. busungwe sp. nov. has not yet been carried out, but given the fact that this species is known for only two specimens from a single locality, it would probably be regarded as Data Deficient.

Remarks

Potamonautes busungwe sp. nov. is superficially similar to several other species in this genus from Uganda that share the following characters: reduced exorbital and epibranchial teeth; a smooth anterolateral margin immediately behind the epibranchial tooth; an incomplete s3/s4 which is deep at the sides but absent in the middle; a male major cheliped with a slim, highly arched dactylus. Ugandan crabs that share this suite of characters include P. rukwanzi , P. williamsi , P. mutandensis ( Chace, 1942) , P. morotoensis and P. imatongensis .

Potamonautes busungwe sp. nov. can be distinguished from P. rukwanzi by its postfrontal crest, which is faint but complete ( Fig. 2A ) (vs distinct and complete in P. rukwanzi ), by its third maxilliped ischium, which lacks a sulcus ( Fig. 2B ) (vs a deep sulcus in P. rukwanzi ) by a sharp and pointed distal tooth on the cheliped merus ( Fig. 2 A–B) (vs a small, blunt and low distal tooth in P. rukwanzi ), and by the G1 terminal article that ends in a slightly upturned tip ( Fig. 6B, E ) (vs an article that turns sharply upward at the tip in P. rukwanzi ). Potamonautes busungwe sp. nov. differs from P. williamsi , P. mutandensis , P. morotoensis and P. imatongensis in that the distal tooth on the inner margin of the cheliped carpus of P. busungwe sp. nov. is strong and pointed (vs a weak, low and blunt distal carpal tooth in these four species). Potamonautes busungwe sp. nov. differs from P. morotoensis and P. imatongensis by the G1 terminal article whose tip is slightly upcurved in P. busungwe sp. nov. ( Fig. 6B, E ) (vs a G1 terminal article with a tip that turns sharply upward in P. morotoensis and P. imatongensis ). Potamonautes busungwe sp. nov. can be distinguished from P. entebbe sp. nov. by an examination of s3/s4, which is reduced to two short notches at the edges and faint in the middle ( Fig. 2B ) (vs V-shaped and deepest at the edges and faintest in the middle in P. entebbe sp. nov.; Fig. 1B ).

Figures

Fig. 2. Potamonautes busungwe sp. nov, holotype, adult ♂, CW 15.9 mm, from Busungwe Island, Lake Victoria, southern Uganda (NHMUK 2017.37). A. Whole animal, dorsal view. B. Whole animal, ventral view. Scale bars: 6.3 mm. Photographs by Phillip Crabb, NHMUK.

Fig. 6. G1, ventral view (A–C) and dorsal view (D–F). A, D. Potamonautes entebbe sp. nov., holotype, adult ♂, CW 35 mm, from Entebbe, southern Uganda (NHMUK 1955.11.8.26). – B, E. P. busungwe sp. nov., holotype, adult ♂, CW 21.5 mm, from Busungwe Island, Lake Victoria (NHMUK 2017.37). – C, F. P. kantsyore sp. nov., holotype, adult ♂, CW 16.8 mm, from Kantsyore Island in the Kagera River, southern Uganda (NHMUK 2017.29). Scale bars: A, D = 2.3 mm; B, E = 3.1 mm; C, F = 3.3 mm.

Fig. 7. Distribution map showing the known localities of Potamonautes entebbe sp. nov. (black triangle), P. busungwe sp. nov. (black circle) and P. kantsyore sp. nov. (black star) in Uganda, East Africa. For exact localities, see text.

Fig. 4. Frontal view of carapace. A. Potamonautes entebbe sp. nov., holotype, adult ♂, CW 35 mm, from Entebbe, Lake Victoria, southern Uganda (NHMUK 1955.11.8.26). – B. P. busungwe sp. nov., holotype, adult ♂, CW 21.5 mm, from Busungwe Island, Lake Victoria,, southern Uganda (NHMUK 2017.37). – C. P. kantsyore sp. nov., holotype, adult ♂, CW 16.8 mm, from Kantsyore Island in the Kagera River, southern Uganda (NHMUK 2017.29). Scale bars: A = 2.34 mm; B = 3.1 mm; C = 3.3 mm. Photographs A–B by Phillip Crabb, NHMUK.

Fig. 5. Frontal view of left and right chelipeds. A–B. Potamonautes entebbe sp. nov., holotype, adult ♂, CW 35 mm, from Entebbe in southern Uganda (NHMUK 1955.11.8.26). – C–D. Potamonautes busungwe sp. nov., holotype, adult ♂, CW 21.5 mm, from Entebbe in southern Uganda (NHMUK 2017.37). – E–F. Potamonautes kantsyore sp. nov., holotype, adult ♂, CW 16.8 mm, from Kantsyore Island in the Kagera River in southern Uganda (NHMUK 2017.29). Scale bar: A–B = 2.3 mm; C–D = 3.1 mm; E–F = 3.3 mm. Photographs A–D by Phillip Crabb, NHMUK.

Fig. 1. Potamonautes entebbe sp. nov., holotype, adult ♂, CW 35 mm, from Entebbe, southern Uganda (NHMUK 1955.11.8.26). A. Whole animal, dorsal view. B. Whole animal, ventral view. Scale bars: 6.3 mm. Photographs by Phillip Crabb, NHMUK.