Potamonautes langi ( 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 : 120-126

publication ID

https://doi.org/ 10.11646/zootaxa.3973.1.4

publication LSID

lsid:zoobank.org:pub:688DC9B0-2EA4-43D5-926A-B184A0A9A7B2

DOI

https://doi.org/10.5281/zenodo.6096908

persistent identifier

https://treatment.plazi.org/id/F02E87F8-1077-FFBF-FF63-BFC9DFE00AE0

treatment provided by

Plazi

scientific name

Potamonautes langi ( Rathbun, 1921 )
status

 

Potamonautes langi ( Rathbun, 1921) View in CoL

Lang’s Freshwater Crab

( Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Potamon (Potamonautes) langi Rathbun, 1921: 430 –433, pl. 32, fig. 14.

Potamonautes View in CoL langi— Balss 1936: 189, 190, fig. 25.

Potamon View in CoL langi— Chace 1942: 215.

Potamonautes (Obesopotamonautes) View in CoL langi— Bott 1955: 256–257, figs. 17, 18, 79a, b, pl. 12, figs. l’a–d. Potamonautes langi View in CoL – Cumberlidge 1998: 200; Ng et al. 2008: 171; Cumberlidge et al. 2009: appendix item 942.

Type material examined. D.R. CONGO. Congo River at Kisangani (0.52° N, 25.20° E), adult male holotype (CW 45, CL 34.5, CH 16, FW 15), 21 Apr. 1915 (J. Chapin and H. Lang) ( AMNH 3353). Congo River at Kisangani, 1 male, 10 females (4 ovigerous) paratypes ( AMNH 3336); 3 females (2 ovigerous), paratypes ( AMNH 3469); Congo River at Kisangani, 3 males, 8 females (5 ovigerous), 1 juvenile ( AMNH 3363); Congo River at Kisangani, 1 male, 7 females (4 ovigerous) (5 males, 10 females (2 ovigerous) sent to USNM), paratypes ( AMNH 3332); Congo River at Kisangani, 2 males, 11 females (5 ovigerous) paratypes ( AMNH 3362); Congo River at Kisangani, 3 males, 16 females (8 ovigerous), 3 juveniles, paratypes ( AMNH 3343); Congo River at Kisangani, 3 males, 5 females (3 ovigerous), paratypes; Congo River at Kisangani, 2 females (both ovigerous) paratypes ( AMNH 3418); 2 females (both ovigerous) paratypes ( AMNH 3393); Congo River at Kisangani, 1 female, paratype, caught on the shore; coll. 14 Aug. 1909; Congo River at Kisangani, 1 female, paratype, coll. 15 Aug. 1909; Congo River at Kisangani, 4 females, paratypes, common under logs in the water, coll. 17 Aug. 1909; Congo River at Kisangani, 1 female, paratypes, coll. 18 Aug. 1909; Congo River at Kisangani, 1 male, paratype, coll. 20 Aug. 1909; Congo River at Kisangani, 1 female, paratype, ovigerous, coll. 21 Aug. 1909; Congo River at Kisangani, 1 female, paratype, coll. 28 Aug. 1909; Congo River at Kisangani, 2 females, paratypes, 1 female, paratype, ovigerous, coll. Feb. 1915; Congo River at Kisangani, 1 male, 13 females (8 ovigerous), paratypes, coll. Apr. 1915; Kisangani, 4 paratypes, (1–30 Apr. 1915) (J. Chapin and H. Lang) ( MCZ CRU- 10614). Other material. D.R. CONGO. Bukama, Katanga (9.15° S, 25.83° E), 2 males, 12 females, Jun. 1935 (P. Brien) ( MRAC 23.937-23.953); Congo River at Kisangani (0.52 N, 25.20 E) ( MRAC 32.872-32.875, 32.879-32.883, 32.895-32.897); Kaleke, Lake Kisale (8.26° S, 26.49° E), 2 males, 1 female ( MRAC 32.010-32.012); Lualaba, Kindu, Maniema (2.93° S, 25.94° E), 1 male, 1 female ( MRAC 32.898-32.900); 9 females, 1 juvenile male; Mobi River, 30 km south of Kisangani (0.22 S, 25.32 E), 3 females ( MRAC 32.901-32.903); Lake Upemba, Haut-Lomami District (8.59° S, 26.51° E), 19 adults, l female subadult, CW 37, 01–07 May 1925 (G. F. de Witte) ( ZSM 1193/1, formerly ZSM 1935, don. MRAC).

Diagnosis. Postfrontal crest complete; exorbital, epibranchial teeth both large forward-pointing spines; anterolateral margin of carapace behind epibranchial tooth with 3 long, pointed teeth ( Fig. 1 View FIGURE 1 B); ischium of third maxilliped lacking visible sulcus ( Fig. 2 View FIGURE 2 C); thoracic sternal sulcus s3/s4 incomplete, deep at sides absent in middle ( Fig. 1 View FIGURE 1 C); carpus of cheliped with 2 subequal long, pointed teeth ( Fig. 1 View FIGURE 1 F,G); G1 terminal article slim, directed outward at a 60° angle to vertical, tapering to up-curved tip ( Fig. 2 View FIGURE 2 D,E,F).

Redescription. Postfrontal crest complete, epigastric lobes continuous with postorbital crests, lateral ends of postorbital crests meeting anterolateral margins. Exorbital, epibranchial teeth both large forward-pointing spines; anterolateral margin between exorbital, epibranchial teeth smooth, curving slightly outward, lacking intermediate tooth; anterolateral margin posterior to epibranchial tooth with 3 long, pointed teeth ( Fig. 1 View FIGURE 1 B). Suborbital margin granular ( Fig. 1 View FIGURE 1 A). Carapace flat ( CH /FW 1.07); front broad, measuring one-third CW (FW/CW 0.33) ( Fig. 1 View FIGURE 1 A). Semi-circular, urogastric, cardiac, posterior, cervical carapace grooves all distinct. Epigastric crests clear, median sulcus between crests short, forked posteriorly ( Fig. 1 View FIGURE 1 B). Carapace sidewall with distinct granular vertical sulcus, ending at longitudinal sulcus, dividing sidewall into 3 parts ( Fig. 1 View FIGURE 1 A). Exopod of third maxilliped with long flagellum, third maxilliped ischium lacking visible sulcus ( Fig. 2 View FIGURE 2 C). Epistomial tooth large, triangular, edges lined by large, round granules ( Fig. 1 View FIGURE 1 A). Mandibular palp two-segmented; terminal segment simple ( Fig. 2 View FIGURE 2 A, B). Thoracic sternal sulcus s2/s3 deep, running horizontally across sternum; thoracic sternal sulcus s3/s4 incomplete, deep at sides absent in middle, sides slanted inward & backward toward anterior margin of sternoabdominal cavity ( Fig. 1 View FIGURE 1 C). Thoracic episternal sulci s4/e4, s5/e5, s6/e6, s7/e7 all visible grooves ( Fig. 1 View FIGURE 1 C). Chelipeds of adult male unequal; fingers of major (right) cheliped long, slender, widely gaping, teeth irregular, those in proximal half bigger than distal half; fingers of minor cheliped long, slender, almost meeting. Propodus of major right cheliped of adult male with swollen palm, fixed finger long, straight; movable finger (dactylus) long, curved Fig. 1 View FIGURE 1 D, E). First, second carpal teeth of inner margin of carpus of cheliped subequal long, pointed teeth. Lateral, medial inferior margins of merus of cheliped granular, with single large pointed distal meral tooth at distal end; superior surface of merus granular Fig. 1 View FIGURE 1 F, G). Abdomen slim, triangular, edges straight ( Fig. 1 View FIGURE 1 I). G1 terminal article about one-third as long as subterminal segment, longitudinal groove visible on dorsal, superior sides (but not on ventral side); G1 terminal article slim, directed outward at a 60° angle to vertical, tapering to up-curved tip ( Fig. 2 View FIGURE 2 D,E,F). G2 terminal article long, flagellum-like ( Fig. 2 View FIGURE 2 G).

Size. Large-size species, adult CW 45 mm and higher.

Color. Dorsal carapace varying from dark brown/green to dark brown/yellow tinged with red, carapace of newly molted animals much lighter, sternum gray/yellow, abdomen white/grey, chelipeds brown/purple. Cryptic color pattern may be protective.

Type locality. Congo River at Kisangani, D.R. Congo.

Habitat. This is a strictly aquatic species that prefers the quieter parts of the Congo River where floating material accumulates and sunken logs offer protection. Potamonautes langi rapidly seeks cover when disturbed, including digging into mud. This species was captured in traditional traps baited with putrid or baked manioc set in deep water with a muddy substratum. These traps also catch fishes, including small silurids and mormyrids.

Conservation status. Potamonautes langi was listed as Least Concern ( IUCN 2003; Cumberlidge et al. 2009) because it is known to occur in six localities and has a wide distributional range of about 140,000 km 2. Furthermore, there is no evidence of a decline in the extent and quality of its habitat and there are no known longterm threats to its habitat from disturbance and pollution ( Cumberlidge 2008a).

Distribution. This species is found in the tributaries of the Upper Congo River at Kisangani and south into the Katanga district of the D.R. Congo ( Fig. 4 View FIGURE 4 ). Most of Bott’s (1955) material listed under P. langi has been included here, despite the fact that he relied on a non-type adult male specimen of P. l angi, which he photographed and illustrated (CW 42 mm, MRAC 23.937, plate XII, fig. 1a–d). Bott (1955) incorrectly recorded this specimen as from “Bukoba, Victoria See” (which is in Tanzania), but the museum label actually reads “Bukama” a locality in the Katanga region of the D.R. Congo. There are also doubts as to the identity of two other geographically isolated specimens from the lower Congo basin and these have not been included here. As an example, Rathbun’s (1921) record of P. langi from Kinshasa (formerly Léopoldville) in the Lower Congo basin based on a female specimen collected on 11 Aug 1909 is doubtful due to the lack of male gonopod, cheliped, and sternum characters. Bott’s (1955) identification of specimens from the Congo River at Matadi in the D.R. Congo (MRAC 21.829-21.831) is also doubtful.

Remarks. This redescription is necessary because Bott’s (1955) redescription was not based on type material, and instead relied on a series of previously unidentified museum specimens (see above). Moreover, Bott’s (1955) classification of the large African genus Potamonautes is also questionable, because he placed P. langi in the subgenus P. ( Obesopotamonautes ), Bott, 1955, as the type species of a subgenus that also included P. obesus (A. Milne-Edwards, 1868) , and P. calcaratus (Gordon, 1929) . However, the redescription of P. ob e s u s and P. calcaratus (Reed & Cumberlidge 2004) casts doubt on a close relationship between P. langi and these two species given the significant morphological differences in the gonopods and somatic characters of these two taxa and P. langi . The most recent molecular phylogeny of the Afrotropical potamonautids ( Daniels et al. 2015) groups P. obesus and P. calcaratus together in a separate clade from P. langi and does not support the recognition of the subgenus P. ( Obesopotamonautes ). Cumberlidge (1997, 1998), Ng et al. (2008), and Cumberlidge et al. (2009) all recognized P. langi as a valid species of Potamonautes and did not recognize the subgenus assignment, but they all made this taxonomic change without explanation.

Comparisons. Potamonautes langi can be recognized by the characters listed above in its diagnosis and by the illustrations and photographs of the holotype ( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 ), including those by Rathbun (1921: 430–433, pl. 32, fig. 14) as Potamon (Acanthopotamonautes) langi . Illustrations and photographs of another specimen from the D.R. Congo can be found in Bott (1955: pl. XII, fig. 1 a–d; fig. 17, 18, 79a) as Potamonautes (Obesopotamonautes) langi .

This species is superficially similar to several other species of Potamonautes with which it shares a number of taxonomic characters. These include a strong and complete postfrontal crest; strong, sharp exorbital and epibranchial teeth; several distinct spines on the anterolateral margins immediately behind each epibranchial tooth ( Fig. 1 View FIGURE 1 B); a third maxilliped ischium that lacks a visible sulcus ( Fig. 2 View FIGURE 2 C); a first carpal tooth on the carpus of the cheliped that is strong and pointed; and a strong and pointed distal meral tooth ( Fig. 1 View FIGURE 1 F, G). Other African freshwater crabs with this suite of characters include P. niloticus (H. Milne Edwards, 1837) (Nile River basin), P. paecilei (A. Milne-Edwards, 1886) (Lower Congo River basin), P. w ar re n i (Calman, 1918), and P. dentatus, Stewart, Coke & Cook, 1995 . The latter are found in river basins in southern Africa.

Potamonautes langi View in CoL differs from P. niloticus View in CoL in that the second carpal tooth on the carpus of the cheliped is as large as the first carpal tooth in P. langi View in CoL ( Fig. 1 View FIGURE 1 F,G) but weak, low and blunt in P. niloticus View in CoL , and the G1 terminal article of P. langi View in CoL is clearly directed outward at 45° to the longitudinal axis of G1 ( Fig. 2 View FIGURE 2 D,E), whereas that of P. niloticus View in CoL is only slightly angled outward at 25° to the longitudinal axis of G1 ( Bott 1955; Cumberlidge 2009; Cumberlidge & Clark 2010). Potamonautes langi View in CoL differs from P. paecilei View in CoL in that P. l a ng i has three large pointed teeth on the anterolateral margin behind the epibranchial tooth ( Fig. 1 View FIGURE 1 B), whereas P. paecilei View in CoL has two large teeth behind the epibranchial tooth on the anterolateral margin, and the sternal sulcus s3/s4 of P. l a ng i is deep at the sides and absent in the middle ( Fig. 1 View FIGURE 1 C), whereas the sternal sulcus s3/s4 of P. paecilei View in CoL is completely absent ( Capart 1954; Cumberlidge 1999).

Potamonautes langi View in CoL differs from P. dentatus View in CoL in that the carapace margin between the exorbital and epibranchial teeth is straight in P. langi View in CoL and there are three large pointed teeth on the anterolateral margin behind the epibranchial tooth ( Fig. 1 View FIGURE 1 B), whereas in P. dentatus View in CoL there is a deep sinus posterior to the exorbital tooth and the pointed teeth on the anterolateral margin behind the epibranchial tooth are all small. The sternal sulcus s3/s4 of P. langi View in CoL is deep at the sides and absent in the middle ( Fig. 1 View FIGURE 1 C) whereas sternal sulcus s3/s4 of P. dentatus View in CoL is deep and complete and forms a distinct V-shape with the bottom of the V meeting the sternoabdominal cavity ( Stewart et al. 1995). Potamonautes langi View in CoL differs from P. w arreni in that P. l a ng i has a slim G1 terminal article that is strongly directed outward at a 45° angle ( Fig. 2 View FIGURE 2 D,E), whereas the G1 terminal article of P. w a r ren i is only slightly directed outward at a 30° angle ( Bott 1955; Daniels et al. 2001).

Four other Afrotropical genera include species that have strong, sharp exorbital and epibranchial teeth and several pointed teeth on the anterolateral margin immediately behind the epibranchial tooth. These are Platythelphusa armata (A. Milne-Edwards, 1887) View in CoL (Lake Tanganyika), Erimetopus brazzae (A. Milne-Edwards, 1886) View in CoL (Lower Congo River basin), Liberonautes chaperi (A. Milne-Edwards, 1887) View in CoL (West Africa), and Sudanonautes faradjensis ( Rathbun, 1921) View in CoL (Central Africa) but they can all be distinguished from species of Potamonautes View in CoL at the genus level ( Cumberlidge 1985, 1995, 1999; Cumberlidge et al. 1999; Cumberlidge & Reed 2004). In contrast to Potamonautes View in CoL , Liberonautes View in CoL and Sudanonautes View in CoL have an intermediate tooth on the anterolateral margin between the exorbital and epibranchial teeth (Cumberlidge 1999); Erimetopus View in CoL has spines on the margins of the merus of P2-P5 (Cumberlidge & Reed 2004); and Platythelphusa View in CoL has a frontal margin that projects forward and is not downturned over the antennular fossae (Cumberlidge et al. 1999).

AMNH

American Museum of Natural History

USNM

Smithsonian Institution, National Museum of Natural History

MCZ

Museum of Comparative Zoology

MRAC

Musée Royal de l’Afrique Centrale

ZSM

Bavarian State Collection of Zoology

Kingdom

Animalia

Phylum

Arthropoda

Class

Malacostraca

Order

Decapoda

Family

Potamonautidae

Genus

Potamonautes

Loc

Potamonautes langi ( Rathbun, 1921 )

Cumberlidge, Neil 2015
2015
Loc

Potamon

Chace 1942: 215
1942
Loc

Potamonautes

Balss 1936: 189
1936
Loc

Potamon (Potamonautes) langi

Rathbun 1921: 430
1921
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