Madagapotamon Bott, 1965

Cumberlidge, Neil & Sternberg, Richard V., 2002, The freshwater crabs of Madagascar (Crustacea, Decapoda, Potamoidea), Zoosystema 24 (1), pp. 41-79 : 65-69

Genus Madagapotamon Bott, 1965

Madagapotamon Bott, 1965: 344-346 , fig. 7, pl. 4, figs 14-17. — Vuillemin 1970: 245-265. — Ng & Takeda 1994: 162, 163, table 1.

TYPE SPECIES. — Madagapotamon humberti Bott, 1965 .

DIAGNOSIS. — Carapace outline heart-shaped, elongated (cl/fw = 3.7), highly arched (ch/fw = 1.7), very wide (cw/fw = 4.9), frontal, posterior margins very narrow (cw 0.25 mm); front sharply deflexed, almost vertical; exorbital tooth large, pointed; epibranchial tooth pointed, smaller; anterolateral margin with four to five pointed teeth behind epibranchial tooth; suborbital, subhepatic, pterygostomial regions of carapace sidewall smooth. Mandibular palp two-segmented, terminal segment simple, no anterior process of any kind at junction between segments; third maxilliped exopod short, just reaching ischium/merus junction; flagellum extremely reduced, stub-like; ischium smooth, vertical sulcus shallow, barely visible. Male sternite s5 smooth, lacking pair of sternal knobs (“boutonpressions” of Guinot 1977, 1978, 1979). Walking legs (p2-p5) extremely long, slender (ratio length merus p5 to cw 0.54). Adult male abdomen oval, egg-shaped. Gonopod 1 terminal article straight, tube-like, tip broad. Terminal article of gonopod 2 a short flagellum, much shorter than the subterminal segment (ratio length terminal article to subterminal segment 0.5).

REMARKS

Madagapotamon is one of the most distinctive genera of all of the Madagascan freshwater crabs and this pale-coloured long-legged, rock-crevice and cave-dwelling species stands apart from all other freshwater crabs on the island. Madagapotamon can be distinguished from all other genera of Madagascan freshwater crabs by the absence of a flagellum on the exopod of the third maxilliped, and by the egg-shaped outline of the adult male abdomen.

Bott (1965) assigned three very different taxa to Madagapotamon : M. humberti , M. gollhardi and M. ankaraharae , apparently because he perceived that all had a mandibular palp with a simple terminal segment. However, the findings of the present work do not support Bott’s (1965) opinion. Madagapotamon ankaraharae bears little resemblance to M. humberti : for example, M. ankaraharae has normal length walking legs, a flagellum on the exopod of the third maxilliped, and a transversely-oval carapace outline. Similarly, the terminal segment of the mandibular palp of M. gollhardi is not truly simple, but actually has a small hard ledge on the terminal segment. The present findings support the removal of M. gollhardi and M. ankaraharae from Madagapotamon , and the recognition of this genus as monotypic for M. humberti , as was suggested by Ng & Takeda (1994).

Madagapotamon humberti Bott, 1965 ( Figs 2E ; 3G ; 4L ; 5H ; 6G ; 7K, L ; 8G ; 10G, H ; 11H )

Madagapotamon humberti Bott, 1965: 344-346 , fig. 7, pl. 4, figs 14-17. — Vuillemin 1970: 245-265. — Ng & Takeda 1994: 162, 163, table 1.

MATERIAL EXAMINED. — Madagascar. Forest of Ankara and of Analamera in northern Madagascar, coll. H. Humblot, 1 ad., holotype of Madagapotamon humberti Bott, 1965 cw 33, cl 24.5, ch 11.5, fw 6 mm ( MNHN-B 5182). — Analamera, northern Madagascar, 1 ad., paratype cw 24.8, cl 18.8, ch 9, fw 5.2 mm ( SMF 2614). — Forest of Ankara and Analamera, 1937/1938, coll. Prof. H. Humbert, 1 paratype, broken up specimen ( MNHN-BP 5174). Handwritten note, probably by Prof. Humbert: “Forêts à feuilles caduques, sur calcaire (lapias) de l’Ankara et de l’Analamera. Crabe arboricole en saison des pluies. Passe probablement la saison sèche dans les fissures très profondes, les avens et les cours d’eau souterrains de ces lapias. XII.1937 et I.1938 ”. — Baie de Diego, Diego- Suarez (now Antsiranana), Antsirana, 230 m altitude, V.1899, coll. R. Decary, 1, dried specimen, 1, dried specimen (broken) ( MNHN-B 5034). Note from M. Decary: “Ces crabes corps et pinces blanc opaque ne sont pas rares sur les rochers, dans la forêt qui recouvre les pentes ouest de la Montagne des Français. Ils sont extrêmement vifs, à la saison sèche, vivent dans les trous des rochers et sortent dès que la pluie commence”. — Nosy-Bé, 2 juv. cw 12.8, 11.6 mm ( ZSM 1163/1), 1 cw 15.8 mm ( SMF 4487).

TYPELOCALITY. — Northern Madagascar, between Ankara and Analamera.

DISTRIBUTION. — Northern Madagascar, between Ankara and Analamera ( Fig. 11H ).

DIAGNOSIS. — As for genus.

REDESCRIPTION

Carapace outline heart-shaped, elongated (cl/fw = 3.7), highly arched (ch/fw = 1.7), very wide anteriorly (cw/fw 4.9), sides tapering sharply; frontal, posterior margins both very narrow (cw 0.2 mm); distinct gap between epigastric, postorbital crests; latter not meeting anterolateral margins; all carapace grooves faint; anterior, posterolateral carapace regions smooth, no granules or carinae; front indented, margin raised, smooth; front sharply deflexed, almost vertical; exorbital tooth large, pointed, epibranchial tooth smaller, point- ed, conspicuous; anterolateral margin between exorbital, epibranchial teeth lacking intermediate tooth; anterolateral margin with four to five pointed teeth behind epibranchial tooth; anterolateral margin continuous with posterolateral margin; vertical sulcus on carapace sidewall running from base of epibranchial tooth to epimeral sulcus, dividing suborbital from hepatic region, carapace sidewall clearly divided into three regions (suborbital, subhepatic, pterygostomial), all smooth. Mandibular palp two-segmented, terminal segment simple, completely lacking anteri- or process of any kind at junction between segments; third maxilliped exopod short, just reaching ischium/merus junction; flagellum extremely reduced, stub-like, ischium smooth, vertical sulcus shallow, barely visible.

Thoracic sternal sulcus s1/s2 not visible, sternal sulci s2/s3, s3/s4 completely crossing sternum, s3/s4 deep at edges, angling backward, middle horizontal, close to anterior margin of sternoabdominal cavity on sternite s4. Male sternite s5 smooth, lacking pair of sternal knobs (“boutonpressions” of Guinot 1977, 1978, 1979). Episternal sulci s4/e4, s5/e5, s6/e6, s7/e7 smooth, no groove visible. Merus, carpus, propodus, dactylus of walking legs (p2-p5) extremely long, slender (ratio length merus p5 to cw 0.54). Dactylus of right, left chelipeds narrow (onequarter height of palm), upper margin smooth, dactylus straight, finger of propodus slim (onethird height of palm) lower margin of propodus of cheliped slightly indented. Fingers of propodus, dactylus with series of small teeth interspersed with three medium teeth; closed fingers enclosing long interspace. Anterior inferior margin of ischium of p1 granular, posterior inferior margin smooth. Inferior margins of merus toothed, distal margin with single pointed distal meral tooth; superior surface of merus smooth. First carpal tooth on inner margin of carpus of cheliped large, pointed; second carpal tooth small, pointed, followed by several smaller teeth. Anterior, posterior margins of propodi of p5 slightly serrated.

Adult male abdomen oval, egg-shaped, not triangular, a6 short, as long as width of distal margin of a6; lateral margins of a2-a7 distinctly convex; telson rounded, dome-shaped. Gonopod 1 terminal article straight, tube-like, tip broad; terminal article short, ratio terminal article to subterminal segment length 0.25; longitudinal groove on terminal article clearly visible on ventral, superior sides, not visible on dorsal side; lateral, medial folds of ventral side of terminal article equal in height, width, medial fold overlapping lateral fold. Subterminal segment of gonopod 1 with rounded disto-medial shoulder-like projection at junction of segments and a rounded baso-medial projection. Lateral flap on ventral side of subterminal segment not reaching basal margin of segment, so opening of chamber for gonopod 2 positioned about one-third of segment length from basal margin. Suture marking junction between terminal article and subterminal segment of gonopod 1 visible dorsally, ventrally; narrow dorsal membrane on dorsal side at junction between segments. Gonopod 2 longer than gonopod 1; terminal article of gonopod 2 a short flagellum, much shorter than subterminal segment of gonopod 2 (ratio length terminal article to subterminal segment 0.5).

Size

The adult size range is from cw 24 to 33 mm. The carapace proportions are given in Table 3.

REMARKS

This genus is closest to Malagasya n. gen., which shares the heart-shaped carapace outline, distinct teeth on the anterolateral margins, and slender elongated walking legs. The two genera can be easily told apart by examination of the mandible and third maxilliped (see above).

There are a number of errors in the characterisation of Madagapotamon by Ng & Takeda (1994), because those authors relied entirely on Bott’s (1965) figures and descriptions rather than on direct examination of specimens. For example, Ng & Takeda (1994: table 1) described the epibranchial tooth of M. humberti as “not visible” when in fact, although small, this tooth is nevertheless visibly distinct without magnification. In addition, their description of the terminal article and subterminal segment of gonopod 1 of M. humberti as not separated by a suture (i.e. fused) is incorrect: the segments are separated by a suture that is clearly visible from the ventral, superior and dorsal views.

Vuillemin (1970) provided excellent ecological notes and a detailed description of the habitat of M. humberti .

Genus Skelosophusa Ng & Takeda, 1994 Skelosophusa Ng & Takeda, 1994: 162 , 163.

TYPE SPECIES. — Madagapotamon gollhardi Bott, 1965 , by original designation.

DIAGNOSIS. — Carapace transversely oval (cw/fw = 3.5-3.6, cl/fw = 2.3-2.8); medium height (ch/fw 1.2- 1.36); exorbital tooth broad, small; epibranchial tooth distinct, rounded, low, continuous with anterolateral margin; anterolateral margin granulated, posterior end curving inward, not continuous with posterolateral margin. Mandibular palp two-segment- ed, terminal segment simple, not bilobed, with small hard ledge-like process at terminal article subterminal segment junction. Third maxilliped ischium with deep vertical sulcus. Sternal suture s3/s4 reduced to two short notches at edges of sternum. Gonopod 1 terminal article short, tube-shaped, tip broad; gonopod 1 terminal article / subterminal segment junction marked by deep sulcus both ventrally, dorsally. Lateral flap on ventral side of subterminal segment long, reaching to basal margin of segment; medial flap on ventral face with distinct distomedial shoulder; opening of chamber for gonopod 2 positioned about one-third of segment length from basal margin. Gonopod 2 terminal article flagellum medium length, ratio length terminal article to subterminal segment 0.5. Walking legs (p2-p5) elongat- ed, slender, ratio length merus p5 to cw 0.5-0.6.

REMARKS

Ng & Takeda (1994) assigned three species to Skelosophusa : S. gollhardi , S. prolixa and S. eumeces . These authors described the terminal segment of the mandibular palp of Skelosophusa as simple (i.e. not bilobed). In fact, the mandibular palp of Skelosophusa is not strictly simple because there is a small hard ledge-like anterior process at the junction between the two segments which these authors clearly illustrated for S. prolixa and S. eumeces ( Ng & Takeda 1994: fig. 6j, k). The type material of S. prolixa and S. eumeces are not in Turin, but are apparently still in the Tokyo National Museum with M. Takeda (P. K. L. Ng pers. comm.). It has proved difficult for us to borrow the specimens in question, and the following account of these two species is, therefore, based only on the photographs and illustrations provided by Ng & Takeda (1994). Without firsthand knowledge of these specimens, it is difficult to elaborate on our doubts concerning the validity of the species assignments of Skelosophusa .

Skelosophusa can be distinguished from all other genera of Madagascan freshwater crabs (except Boreas n. gen.) by the small ledge-like anterior process of the terminal segment of the mandibular palp. Skelosophusa can be distinguished from Boreas n. gen. as follows. The ischium of the third maxilliped of Skelosophusa has a deep vertical sulcus, whereas in Boreas n. gen. the ischium is smooth, and the walking legs of Boreas n. gen. are of normal length, whereas those of Skelosophusa are slender and remarkably elongated.

Figures

FIG. 2. — Dorsal view of the carapace of adult males of Madagascan freshwater crabs (A-C based on Ng & Takeda 1994); A, Skeleosophusa gollhardi (Bott, 1965), holotype (MNHN B-5165); B, S. prolixa Ng & Takeda, 1994, holotype, (MRSN); C, S. eumeces Ng & Takeda, 1994, holotype, (MRSN); D, Boreas uglowi n. gen., n. sp., holotype (MNHN B- 11292); E, Madagapotamon humberti Bott, 1965; F, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002, holotype, (AMNH 17833). Scale bar: A, 7.2 mm; B, 7.1 mm; C, 6.5 mm; D, 9 mm; E, 9.4 mm; F, 6 mm.

FIG. 3. — Inferior view of the sternum of adult males of Madagascan freshwater crabs; A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Malagasya antongilensis (Rathbun, 1905) n. comb.; F, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb., G, Madagapotamon humberti Bott, 1965; H, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; I, Boreas uglowi n. gen., n. sp. Scale bar: A, 11.7 mm; B, 17.2 mm; C, 15.9 mm; D, 14.5 mm; E, 10.2 mm; F, 7 mm; G, 9.6 mm; H, 6.4 mm; I, 9.1 mm.

FIG. 4. — Left mandible of Madagascan freshwater crabs, frontal view showing the palp (J, K based on Ng & Takeda 1994); A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Malagasya antongilensis (Rathbun, 1905) n. comb.; F, M. goodmani (Cumberlidge, Boyko & Harvey, 2000) n. comb.; G, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2000; H, Boreas uglowi n. gen., n. sp.; I, Skeleosophusa gollhardi (Bott, 1965); J, S. prolixa Ng & Takeda, 1994; K, S. eumeces Ng & Takeda, 1994; L, Madagapotamon humberti Bott, 1965. Scale bar: A-I, K, L, 1.0 mm; J, 1.25 mm.

FIG. 5. — Left third maxilliped of Madagascan freshwater crabs, frontal view (J, K based on Ng & Takeda 1994); A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Malagasya antongilensis (Rathbun, 1905) n. comb.; F, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb.; G, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; H, Madagapotamon humberti Bott, 1965; I, Skelosophusa gollhardi (Bott, 1965); J, S. prolixa Ng & Takeda, 1994; K, S. eumeces Ng & Takeda, 1994; L, Boreas uglowi n. gen., n. sp. Scale bar: A-D, 5.0 mm; E-L, 3.5 mm.

FIG. 6. — Superior view of the carpus of the cheliped (pereiopod 1) of adult males of Madagascan freshwater crabs (J, K based on Ng & Takeda 1994); A Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Malagasya antongilensis (Rathbun, 1905) n. comb.; F, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb.; G, Madagapotamon humberti Bott, 1965; H, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; I, Skeleosophusa gollhardi (Bott, 1965); J, S. prolixa Ng & Takeda, 1994; K, S. eumeces Ng & Takeda, 1994; L, Boreas uglowi n. gen., n. sp. Scale bar: A-D, 5.5 mm; E-L, 3.5 mm.

FIG. 7. — Superior and inferior views of the merus of the cheliped (pereiopod 1) of adult males of Madagascan freshwater crabs; A, B, Hydrothelphusa agilis A. Milne-Edwards, 1872; C, D, H. madagascariensis (A. Milne-Edwards, 1872); E, F, H. bombetokensis (Rathbun, 1904); G, H, H. goudoti (H. Milne Edwards, 1853) n. comb.; I, J, Malagasya antongilensis (Rathbun, 1905) n. comb.; K, L, Madagapotamon humberti Bott, 1965; M, N, Skelosophusa gollhardi (Bott, 1965); O, P, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; Q, R, Boreas uglowi n. gen., n. sp. Scale bar: A-H, 5.0 mm; I-T, 3.0 mm.

FIG. 8. — Last walking leg (pereiopod 5) of adult males of Madagascan freshwater crabs (H based on Ng & Takeda 1994); A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Boreas uglowi n. gen., n. sp.; F, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; G, Madagapotamon humberti Bott, 1965; H, Skelosophusa prolixa Ng & Takeda, 1994; I, Malagasya antongilensis (Rathbun, 1905) n. comb.; J, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb. Scale bar: A-D, 5.0 mm; E-L, 2.6 mm.

FIG. 10. — Right first gonopod (dorsal and ventral views) of adult males of Madagascan freshwater crabs; A, B, Boreas uglowi n. gen., n. sp.; C, D, Malagasya antongilensis (Rathbun, 1905) n. comb.; E, F, Skeleosophusa gollhardi (Bott, 1965); G, H, Madagapotamon humberti Bott, 1965; I, J, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002. Scale bar: 4.0 mm.

FIG. 11. — Summaries of the known distribution of the Madagascan freshwater crabs; A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853); E, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; F, Malagasya antongilensis (Rathbun, 1905) n. comb.; G, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb.; H, Madagapotamon humberti Bott, 1965; I, Skelosophusa gollhardi (Bott, 1965); J, S. prolixa Ng & Takeda, 1994; K, S. eumeces Ng & Takeda, 1994; L, Boreas uglowi n. gen., n. sp.