Potamonautes obesus
Creators: name: Reed, Sadie K.
name: Cumberlidge, Neil
Publisher: name: Zenodo
Year: 2004
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Potamonautidae
Potamonautes
Potamonautes obesus

description: Potamonautes obesus (A Milne­Edwards, 1868) (Figs. 1­8, 17­25, 30)
Thelphusa obesa A. Milne­Edwards, 1868: 86, pl. 20, fig. 1­4.
Thelphusa obesa: A. Milne­Edwards, 1869: 178.
Telphusa obesa: Hilgendorf, 1879: 801.
Thelphusa obesa: A. Milne­Edwards, 1887: 146.
Thelphusa obesa: Pfeffer, 1889: 33.
Telphusa obesa: Hilgendorf, 1891: 20.
Potamon (Potamonautes) obesum: Ortmann, 1897: 303, 305.
Telphusa obesa: Hilgendorf, 1898: 16.
Potamon obesum: de Man, 1898: 434, 437.
Potamon (Potamonautes) bottegoi, de Man 1898: 262­270, fig. 3.
Potamon (Potamonautes) bottegoi: de Man, 1898: 436.
Potamon (Potamonautes) obesus: Rathbun, 1904: pl. 15, fig. 8, 9.
Potamon (Potamonautes) obesus: Rathbun, 1905: 180, fig. 45.
Potamon (Potamonautes) bottegoi: Rathbun, 1905: 180.
Potamon (Potamonautes) obesus: Sendler, 1912: 199.
Potamon (Potamonautes) obesus: Bouvier, 1921: 49.
Potamon (Potamonâutes) bottegoi: Colosi, 1925: 2.
Potamon (Potamonautes) bottegoi: Parisi, 1925: 98.
Potamonautes obesus: Balss, 1929: 348.
Potamon (Potamonautes) bottegoi: Rathbun, 1933: 258.
Potamon (Potamonautes) bottegoi: Rathbun, 1935: 26.
Potamonautes obesus: Barnard, 1935: 484.
Potamon (Potamonautes) obesus: Chace, 1942: 190.
Potamon bottegoi: Chace, 1942: 208.
Potamon (Potamonautes) obesus: Barnard, 1950: 192.
Potamon (Potamonautes) bottegoi: Barnard, 1950: 192, fig. 34 f, g.
Potamon (Potamonautes) obesus: Capart, 1954: 841, fig. 36, 17
Potamonautes (Obesopotamonautes) obesus obesus: Bott, 1955: 257–259, pl. XXII fig. 2a–d, fig. 19, 80.
Potamonautes (Obesopotamonautes) obesus obesus: Pretzmann, 1977: 238, figs 7–12.
Potamonautes obesus: Cumberlidge, 1997: 580.
Potamonautes bottegoi: Cumberlidge, 1997: 581–582.
Potamonautes bottegoi: Cumberlidge, 1998: 198.
Potamonautes obesus: Cumberlidge, 1998: 202–203.
Type material: TANZANIA: Thelphusa obesa A. Milne­Edwards, 1868, dried, form II adult male, holotype (designated here, cw 50.6 mm, cl 39.5 mm), Zanzibar, (Grandidier) (MNHN­B 4632). Photographs of the holotype and of an ovigerous female (cw 49.5 mm) from Nyassa were provided by Rathbun (1904, 180–182, plate VII, figs. 8, 9), and the holotype was illustrated by Capart (1954). SOMALIA: de Man (1898) described Potamon (Potamonautes) bottegoi de Man, 1898 based on four sub­adult males from Matago I Bool (=Bohol), between Brava and Lugh (Captain Bottego), x.1895; one of these males, a paratype (cw 27 mm) (ZMA 102868) was examined in the present study. Bott (1955) listed the ‘type’ of Potamon (Potamonautes) bottegoi as the specimen with the following dimensions: cw 31, cl 24, ch 13, fw 10 mm. Pretzmann (1977) referred to all of the specimens from Matago I Bool as the ‘holotype’, but did not specify an individual specimen.
Additional material: SOMALIA: Ola Uager, 2 adult males (cws 44, 42 mm), iii.1970 (M. Vannini) (NHMW 4366); Lac Badana, form II adult male (cw 52 mm), major cheliped length 61.5 mm (>cw), x.1971 (M. Vannini) (NHMW 4367); Afmedu, form II adult male (cw 59.6 mm), major cheliped length 68.6 mm (>cw), 3 males (cws 42, 41, 39 mm), subadult female (cw 38 mm), viii.1970 (M. Vannini) (NHMW 4368); Giohar, juvenile male (cw 28 mm), subadult female (cw 35 mm), viii.1971 (M. Vannini) (NHMW 4370); Bur Akaba, subadult female (cw 37 mm), x.1971 (M. Vannini) (NHMW 4371); Gelib, juvenile, 1962 (Lanza) (NHMW 4372); Baidoa, subadult female (cw 34 mm), 1959 (A.M. Simonetta) (NHMW 4373); Baidoa, form II adult male (cw 54 mm), major cheliped length 58 mm (>cw), x.1971 (M. Vannini) (NHMW 4374). KENYA: Southeast, Silver Beach, 5 km north of Mombasa, juvenile female (cw 14.5 mm) 31.vi.1987 (M. Lödl) (NHMW 13351); Tana River, juvenile female (damaged) (W.A. Chanler) (USNM 20647); Lorian Marsh, adult male (cw 41.9, cl 31.3, ch 17.9, fw 12.9), adult female, ovigerous (cw 32.6, cl 24.7, ch 13.7, fw 10.7), juvenile (cw 14.7, cl 10.4, ch 6.6, fw 5.2), juvenile (cw 14.8, cl 11.4, ch 7.3, fw 5.6) (USNM 59367); Voi, juvenile female (cw 21.9, cl 17.9, ch 9.4, fw 8.2), juvenile male (cw 19.9, cl 15.5, ch 8.6, fw 7.7), 7.iv.1934 (A. Loveridge) (USNM 70910); adult male (cw 42.2, cl 32.6, ch 20.9, fw 15.0), (NMU 7.2001 a.1). TANZANIA: Mlali, near Morogoro, Uluguru Mountains, adult male (cw 49.1, cl 36.7, ch 21.7, fw 16.1 mm), 20.v.1968 (J.N. Raybould) (NMU TRW 1968 a.06); Mlali, near Morogoro, Uluguru Mountains, adult male (cw 41.3, cl 30.5, ch 17.5, fw 14.7 mm), adult female (cw 43.4, cl 32.8, ch 18.2, fw 15 mm), 20.v.1968 (J.N. Raybould) (NMU TRW 1968 b.06); adult male (cw 42, cl 31.9, ch 18.4, fw 14.5 mm), USDM campus, Dar es Salaam, 6.iv.1986 (NMU KMH 3455); Dam at Handemi, between Pare Mountains and Uluguru Mountains, 4 juveniles (cw 8.9, cl 7.7, ch 4.2, fw 3.6 mm; cw 12, cl 8.9, ch 5.1, fw 4.5 mm; cw 18, cl 14.3, ch 8.7, fw 6.7 mm; cw 24.2, cl 18.7, ch 11.4, fw 8.5 mm), 2 females (cw 33.5, cl 25.9, ch 15.3, fw 11.1 mm); cw 36.8, cl 28.4, ch 16.9, fw 13.8 mm), male (cw 40.8, cl 30.9, ch 19.4, fw 13.8 mm), 19.ii.1962 (NMU TRW EA62.37); Mlali, south of Morogoro, Uluguru Mountains, 4 females (cw 34.1, cl 23.9, ch 14.7, fw 11.5 mm; cw 33.9, cl 24.8, ch 15, fw 12.1 mm; cw 41.7, cl 30.3, ch 18.3, fw 14.5; cw 48.1, cl 36.3, ch 20.3, fw 17 mm), juvenile (cw 12.2, cl 9.5, ch 5.3, fw 4.3 mm) 21.ii.1962 (NMU TRW EA62.40); East Usambara Mountains, 2 females (cw 35.9, cl 27.3, ch 16, fw 12.9 mm; cw 39, cl 29.5, ch 16.8, fw 13.5 mm), 1970 (J.N. Raybould) (NMU TRW 1970.10); Muheza, near Amani, East Usambara Mountains, temporary stream, juvenile (cw 23, cl 17.7, ch 10.6, fw 8.1) (NMU TRW 1962.07); Kihurio, Gonja, South Pare Mountains, near Saseni river, 2 juveniles (cw 15.3, cl 12.2, ch 7.3, fw 6.2 mm; cw 8.6, cl 7.5, ch 4.3, fw 3.5 mm), 1962 (NMU TRW EA62.28); RS Nambunjo, Muengei, Maturbi, female (cw 42.7, cl 31.6, ch 19.1, fw 15.6 mm), male (cw 27.3, cl 20.2, ch 12.9, fw 9.3 mm), 4 juveniles (cw 18, cl 14.1, ch 8.2, fw 6.6 mm; cw 14.3, cl 12.2, ch 6.8, fw 4.9 mm; 2 damaged), xi.1989 (J. Kingdon) (NMU 11.1989.6); Litipo Forest Reserve, Lindi District, 39º29'E, 6º02'S, female (cw 40.1, cl 30.2, ch 17.8, fw 12.9 mm), (Frontier Tanzania) (NMU 1990.2); Kiono Forest, Makange Forest Reserve, Bagamoyo District, 2 juveniles (cw 28, cl 17.3, ch 9.6, fw 7.8 mm; cw 26.4, cl 20.8, ch 11.3, fw 9.9 mm), female (cw 36.4, cl 27.34, ch 16, fw 12.8 mm) iii.1990 (Frontier Tanzania) (NMU 3.1990.1–3); Tono'omba Forest Reserve, Yiewa District, Undi region, 39º01.E 8º25.S, 150–540 m asl, male (cw 44, cl 32.3, ch 18.7, fw 14.8 mm), 4 juveniles (cw 25.7, cl 19.5, ch 11.5, fw 9.2 mm; cw 24.8, cl 19.1, ch 11.3, fw 8.1 mm; cw 20, cl 15.2, ch 9.2, fw 7.4 mm; cw 17.4, cl 13.3, ch 17.5, fw 6.4 mm) vi–ix.1992 (Frontier Tanzania) (NMU 6 – 9.1992.1–5); Genda­Genda South Forest, Handeni District, 38º38.E 5º33.S, juvenile (cw 16.1, cl 12.6, ch 7.6, fw 6.6 mm), male (cw 40.2, cl 30.56, ch 19, fw 13.9 mm), 29.vii–18.ix.1991 (Frontier Tanzania) (NMU 29.7 ­ 18 ­9.1991.1­2); Genda Genda Dry Forest 58°38.E 5°32.S, adult male (cw 46.1, cl 34.7, ch 24.6, fw 16.7 mm), 2 ovigerous females (cw 41.1, cl 31.1, ch 17.1, fw 14.7; cw 37.9, cl 27.7, ch 16.3, fw 12.3 mm), subadult male (cw 34.5, cl 27.0, ch 17.2, fw 12.6 mm), 2 juvenile males (cw 32.3, cl 24.6, ch 15.7, fw 11.65; cw 24.3, cl 18.9, ch 11.65, fw 9.4 mm), juvenile female (cw 18.0, cl 14.3, ch 8.35, fw 6.5 mm), 2 juveniles (damaged), (Frontier Tanzania) (NMU 7.2001 b.1– 9); Mount Tongwe, Muweza District, Tanga region, male (cw 38.9, cl 29.4, ch 19.5, fw 14.7 mm), 10.ii.1992 (Frontier Tanzania) (NMU 10.02.1992.1); Kazimzumbwi Forest Reserve, Kisarawe District, 39º03.E 6º57.S, 2 females (cw 30.5, cl 23.5, ch 13.4, fw 11.8 mm; cw 30.4, cl 23.6, ch 13.6, fw 11 mm), male (cw 27.1, cl 21.2, ch 12.5, fw 10.5 mm), 3 juveniles (cw 17.7, cl 14.7, ch 8.5, fw 7.1 mm; cw 14.1, cl 10.2, ch 5.9, fw 5.3 mm; cw 15.4, cl 12.5, ch 6.5, fw 5.8 mm), i–ii.1991 (Frontier Tanzania) (NMU 1 – 2.1991.1–6); Kazimzumbwi Forest Reserve, Kisakawe District, 39º03.E 6º57.S, male (cw 28, cl 22.1, ch 13.9, fw 10.8), female (cw 27.2, cl 21, ch 12.2, fw 9.5 mm), 7 juveniles (cw 17.5, cl 13.9, ch 7.5, fw 6.1 mm, damaged; cw 13.6, cl 10.7, ch 5.8, fw 5 mm; cw 12.8, cl 10, ch 5.7, fw 4.7 mm; cw 11.3, cl 9.2, ch 5.1, fw 4.7 mm; cw 11, cl 8.8, ch 5.1, fw 4.7 mm; cw 10.8, cl 8.8, ch 5.5, fw 3.9 mm; one damaged), i–ii.1991 (Frontier Tanzania) (NMU 1 – 2.1991.1–9); Matumbi Forest, Rifiji District, male (cw 49.1, cl 36.3, ch 23.4, fw 15.5 mm), adult female (damaged), juvenile female (cw 14.0, cl 10.75, ch 5.9, fw 5.6) (Frontier Tanzania) (NMU 1990.1); stream near Saggo­Nganga? Nyanga?, Njanga?, adult female, ovigerous (cw 36.8 mm), subadult female (cw 33.1 mm) (Fülleborn) (ZSM 1518 /1); adult female (cw 35.5 mm), subadult female (cw 25.8 mm) (ZSM 1518 /2); Tendaguru, water hole, adult female (cw 52.2 mm), Reck coll. (ZSM 1518 /4); Kilwa, adult female, ovigerous (cw 47.8 mm) (Eimer) (ZSM 1518 /3); Pemba Island, subadult female (cw 29.5 mm), juvenile male (cw 19.3 mm) (Lenz) (ZSM 1200 /2); vicinity of Nyassa and Lake Tanganyika, adult female, ovigerous (cw 40.3, cl 28.9, ch 17, fw 12.9) (USNM 30010). MALAWI: Mhandwe stream, 20 km south of Monkey Bay on Lake Malawi, female (cw 38.3, cl 26.7, ch 14.9, fw 11.9 mm), 14.vi.1971 (D.H. Eccles) (NMU TRW 1972.06).
Diagnosis. Carapace of adult high (ch/fw 1.3), smooth, rounded, epibranchial corner sloping downward; epibranchial tooth small but pointed, positioned well behind postfrontal crest; sidewall clearly in 4 parts; episternal sulcus s4/e4, s7/e7 incomplete, s5/e5, s6/e6 complete, dactylus of major cheliped of form I adult male (cw 39–42 mm, Fig. 19, 20) flat, broad, palm very high; dactylus of major cheliped of form II adult male (cw 43–59.6 mm, Fig. 21) highly curved, slim, elongated (propodus of cheliped longer than cw), palm very high; terminal article of gonopod 1 directed outward at a 45° angle to vertical, slim, tapering to slightly upcurved tip; lateral fold on terminal article wider, higher than medial fold; subterminal segment of gonopod 1 columnar, broad from base to apex.
Redescription. The dorsal carapace and first gonopod of the adult male holotype from Zanzibar, Tanzania (MNHN­B4632) were illustrated by Capart (1954). This specimen is dried, so the following description is based on a form II adult male (cw 49.1 mm, NMU TRW 1968.06, Figs. 1–8) from Mlali, near Morogoro, Uluguru Mountains, Tanzania. Carapace relatively wide (cw/fw 3.0), highly arched (ch/fw 1.0); front slightly indented, slightly deflexed, medium width (about one third cw, fw/cw 0.3). Postfrontal crest present but faint, epigastric lobes continuous with postorbital crests, ends curving back towards epibranchial teeth, but not quite meeting. Dorsal surface of carapace smooth; semi­circular, urogastric, cardiac, cervical grooves faint; mid­groove of postfrontal crest short, deep, forked at posterior end. Exorbital tooth small, low; epibranchial tooth small, pointed, positioned well behind postorbital crests; anterolateral margin behind epibranchial tooth raised, smooth continuous with posterolateral margin (not curving inward over carapace at posterior end); posterior margin of carapace about one third as wide as carapace. Suborbital, subhepatic, pterygostomial regions of carapace sidewall either faintly granular or smooth; sidewall in four parts, vertical sulcus on sidewall granular, beginning on anterolateral margin close to exorbital tooth, dividing suborbital region from hepatic region, vertical sulcus continuing across pterygostomial region, dividing it into two parts. Ischium of third maxilliped smooth, lacking vertical groove, exopod with long flagellum. Second thoracic sternal sulcus s2/s3 deep, completely crossing sternum, third thoracic sternal sulcus s3/s4 incomplete, sides deep, angled inward, middle shallow, distinct bulges on s4 where chelipeds articulate. Episternal sulcus s4/e4, s7/e7 incomplete, s5/e5, s6/e6 distinct. Male abdomen a broad­based triangle, side edges curving slightly inward; sides of telson slightly indented.
Chelipeds highly unequal; dactylus of major cheliped of form I adult male (cw 38–42 mm, Fig. 19, 20) flat, broad, narrow interspace, propodus of cheliped shorter than cw, palm very high; dactylus of major cheliped of form II adult male (cw 49.1 mm, Fig. 21) highly curved, slim, enclosing long oval interspace, elongated, propodus of cheliped longer than cw, palm very high; propodus of right cheliped of form II male (cw 49.1 mm) higher (22 mm), longer (51.3 mm), than that of left cheliped (12.6 mm, 29.5 mm, respectively); teeth along inner margin of dactylus weak, blunt; finger of propodus long (extending beyond dactylus), lined by small teeth interspersed with three larger pointed molars; dactylus of minor (left) cheliped straight, extending beyond finger of propodus; fingers of dactylus, propodus of left cheliped with short pointed teeth along inner margins, touching when closed. Palms of both chelipeds smooth. Inner margin of carpus of cheliped with two teeth, first large, blunt, directed forward, second blunt, approximately half size of first. Inner margin of merus of cheliped with smooth oval surface (meral tympanum); medial, inferior margin of merus of cheliped smooth with single large distal tooth; superior surface of merus with rows of prominent, rough grains. Merus P5 longer than fw; propodi of P4, P5 short, wide (shorter than fw), anterior, posterior margins of propodi of P5 clearly serrated; dactylus of P4 long, dactylus of P5 very short, shortest of walking legs.
Terminal article of gonopod 1 about one third as long as subterminal segment; entire terminal article directed outward at a 45° angle to vertical, slim, tapering to slightly upcurved tip; lateral fold on terminal article wider, higher than medial fold; longitudinal groove visible on superior side of terminal article, ventral side of subterminal segment; medial, lateral margins of subterminal segment fringed by short setae; subterminal segment columnar, broad from base to apex; dorsal membrane visible on subterminal segment. Gonopod 2 longer than gonopod 1; terminal article of gonopod 2 long, flagellumlike, over one half as long as subterminal segment.
Size. The adult size range based on measurements of the specimens from Tanzania, Kenya and Somalia is between cws 39–59.6 mm (although one adult ovigerous female from Somalia measured cw 32 mm).
Variation. The chelipeds of P. obesus change dramatically as crabs grow (Figs. 17– 21), with allometric growth producing heterochely, where the right (major) cheliped is longer and higher than the left (the minor cheliped). Changes in the propodus and dactylus of the major cheliped are the most dramatic. We recognise here two distinct forms of the major cheliped of adult males, which we term form I and form II. The major cheliped of form I adult males (e.g., cw 38–42 mm, Fig. 19, 20) shows the following developments. The palm of the propodus is swollen, very high, and the inferior margin of the propodus forms a smooth downward curve extending to the tip of the fixed finger, which is very broad and flat; the dactylus of the major cheliped is also broad and flat along its length. The palm of the propodus of the major cheliped of form II adult males (e.g., cw 49.1 mm, Fig. 21) is swollen, high and the inferior margin forms a smooth downward curve extending to the tip of the fixed finger, which is broad, flat, and elongated. The fixed finger of the propodus of the major cheliped of form II males is elongated, so that the propodus length is longer than the carapace width; the dactylus of form II males is highly curved, slim and elongated, and encloses a large oval interspace.
Characters that vary with age and with geographical locality include the degree of granulation on the carapace sidewall (which ranges from heavily granulated to completely smooth); and the degree of definition of the postfrontal crest (which varies between sharpedged in subadults to faint in adults).
Type locality. Potamonautes obesus: Zanzibar, Tanzania, East Africa. Potamon (Potamonautes) bottegoi de Man, 1898: Matago I Bool (Bohol), Somalia.
Distribution. The distribution of all known localities of P. obseus is summarized in Fig. 28. Potamonautes obesus is found in Somalia, Kenya, Tanzania (principally in the coastal region, plus Zanzibar and Pemba islands), and Malawi. Barnard (1950) reports that this species occurs in Harare, Zimbabwe.
Comments. Bott (1955) considered Potamonautes obesus to be a senior synonym of Potamon (Potamonautes) bottegoi de Man, 1898, and this view is accepted here. Potamonautes obesus from Tanzania and Somalia was found to share a number of diagnostic characters (see above) with the subadult paratype of P. (P.) bottegoi from Somalia, and the two taxa are considered here to belong to the same species. For example, the dorsal surface of the carapace of both taxa is smooth and highly vaulted, and the major cheliped of form II adult males is longer than the carapace width. In addition, there is no vertical groove on the ischium of the third maxilliped, the male abdomen outline forms a broad­based triangle, all episternal grooves are present to some degree, and the carapace sidewalls are divided by surface grooves into four parts. Differences between the male major cheliped and gonopod 1 of P. obesus from Tanzania and of the subadult types of P. (P.) bottegoi from Somalia can be attributed to differences between these characters in subadult males and form I and form II adult males, rather than to differences at the species level.
Natural history. Williams et al. (1964) provide field notes on the habitat of P. obesus found in an arid area close to Mount Meru in northern Tanzania. Those authors collected specimens of P. obesus together with Deckenia mitis Hilgendorf, 1898 (Deckeniidae) from wetland areas where the standing surface water was relatively warm and stagnant. Williams et al. (1964) reported that P. obesus and D. mitis were dug out from their burrows sited near the waters edge, and were rarely seen actually in the water. The burrows of these crabs often cause extensive damage to drainage ditches. Although data regarding the current population trends of P. obesus are unavailable, this species has a relatively wide distribution, is well represented in museum collections, and has been collected in the past ten years. For these reasons we would judge its conservation status to be in the Least Concern category of the Red List Assessment (IUCN 2001).
description: Published as part of Reed, Sadie K. & Cumberlidge, Neil, 2004, Notes on the taxonomy of Potamonautes obesus (A Milne-Edwards, 1868) and Potamonautes calcaratus (Gordon, 1929) (Brachyura: Potamoidea: Potamonautidae) from eastern and southern Africa, pp. 1-20 in Zootaxa 418 (1) on pages 3-11, DOI: 10.11646/zootaxa.418.1.1, http://zenodo.org/record/5027898