Malagasya, Cumberlidge & Sternberg, 2002

Cumberlidge, Neil & Sternberg, Richard V., 2002, The freshwater crabs of Madagascar (Crustacea, Decapoda, Potamoidea), Zoosystema 24 (1), pp. 41-79 : 59-61

Genus Malagasya n. gen.

Potamon (Parathelphusa) Rathbun, 1905: 265 , 266, fig. 21, pl. 12, fig. 5. — Cumberlidge 1998: 210 [non Parathelphusa H. Milne Edwards, 1853].

Hydrothelphusa (Acanthothelphusa) Bouvier, 1921: 52 [non Acanthothelphusa Ortmann, 1893].

Potamon (Geothelphusa) Balss, 1929: 355 , fig. 21, fig. 2 [non Geothelphusa Stimpson, 1858].

Gecarcinautes Bott, 1960: 337 , 338, figs 1-3, pl. 1, figs 1-3; 338, pl. 1, fig. 45. — Vuillemin 1972: 135- 166. — Ng & Takeda 1994: 163 [non Gecarcinautes Bott, 1965 = Potamonautes Macleay, 1838 ].

TYPE SPECIES. — Potamon (Parathelphusa) antongilensis Rathbun, 1905 , by present designation.

ETYMOLOGY. — Malagasya is a noun in apposition derived from Malagasy, for the Malagasy Republic. Gender feminine.

DIAGNOSIS. — Carapace outline heart-shaped, elongated (cl/fw = 3), high (ch/fw = 1.6), very wide anteriorly (cw/fw = 3.8), frontal, posterior margins narrow (cw 0.3 mm); distinct gap between epigastric, postorbital crests; front sharply deflexed, almost vertical; exorbital tooth pointed; epibranchial tooth pointed, smaller; anterolateral margin between exorbital, epibranchial teeth lacking intermediate tooth; anterolateral margin behind epibranchial tooth with five or more large pointed teeth. Mandibular palp two-segmented, terminal segment with enlarged anterior process (about 0.5 as big as terminal segment) at junction between segments; third maxilliped exopod with long flagellum, ischium with deep vertical sulcus. Thoracic sternal sulcus s2/s3 horizontal, completely crossing sternum, s3/s4 either horizontal or V-shaped. Episternal sulci s4/e4, s5/e5, s6/e6, s7/e7 smooth, all lacking visible groove. Walking legs (p2-p5) extremely long, slender (ratio length merus p5 to cw 0.52). Adult male abdomen slim, triangular. Deep suture between terminal article and subterminal segment of gonopod 1 visible dorsally, ventrally; dorsal membrane broad. Long medial flap on ventral side of subterminal segment of gonopod 1, flap reaching to basal margin of segment; lateral flap on ventral face of subterminal segment of gonopod 1 with distinct disto-medial shoulder; opening of chamber for gonopod 2 on subterminal segment of gonopod 1 positioned about one-quarter of segment length from basal margin. Gonopod 2 terminal article flagellum medium length, ratio length terminal article to subterminal segment 0.6.

REMARKS

Malagasya n. gen. is the commonest and most widely distributed of the long-legged freshwater crabs of Madagascar. The bilobed mandibular palp terminal segment of Malagasya n. gen. is similar to that seen in Hydrothelphusa and Marojejy , but Malagasya n. gen. is easily distinguished from both by its heart-shaped carapace outline. Other distinguishing characters are the walking legs of Hydrothelphusa (which are not elongated), and the chelipeds of Marojejy (which are strikingly elongated). Malagasya n. gen. is established to accommodate two species: M. antongilensis and M. goodmani previously assigned to Gecarcinautes (see above).

Malagasya n. gen. superficially resembles Globonautes macropus (Rathbun, 1898) from West Africa in the heart-shaped carapace outline, the highly deflexed almost vertical front, and the extremely elongated walking legs ( Cumberlidge 1991, 1999). The two genera can be distinguished as follows: the anterolateral margins of the carapace of Malagasya n. gen. are clearly toothed, whereas these margins in Globonautes are smooth; the anterior process on the terminal segment of the mandibular palp of Malagasya n. gen. is about half as large as the posterior lobe, whereas this process is large and subequal in Globonautes ; and the exopod of the third maxilliped of Malagasya n. gen. has a long flagellum, whereas in Globonautes the exopod lacks a flagellum.

Malagasya n. gen. can be distinguished from Hydrothelphusa and Boreas n. gen. by the length of the walking legs, which are of normal length in Hydrothelphusa and Boreas n. gen. and slender and elongated in Malagasya n. gen. Malagasya n. gen. can be distinguished from the other Madagascan genera with slender, elongated walking legs (e.g., Madagapotamon , Skelosophusa and Marojejy ) as follows. Malagasya n. gen. is close to Madagapotamon because both share the following suite of characters: an elongated, heart-shaped carapace outline, very narrow anterior and posterior margins of the carapace, sharply-pointed exorbital and epibranchial teeth, a row of small teeth on the anterolateral margin, a sharply deflexed, and an almost vertical front. The two taxa can be easily distinguished by differences in the terminal article of the mandibular palp (which in Malagasya n. gen. is bilobed with a medium-sized anterior process whereas that of Madagapotamon is simple and lacks an anterior process), by the exopod of the third maxilliped (which in Malagasya n. gen. is a long flagellum, whereas in Madagapotamon the flagellum is lacking), and by the shape of the adult male abdomen (which is triangular in Malagasya n. gen. but oval and egg-shaped in Madagapotamon ).

Malagasya n. gen. can be distinguished from Marojejy by the length of the eyestalks (which taper sharply, and have a reduced cornea in Marojejy , and are of normal length with a large cornea in Malagasya n. gen.); by the length of the merus of the chelipeds (which is extremely elongated in Marojejy and of normal length in Malagasya n. gen.); by the exorbital and epibranchial teeth (which are low and blunt in Marojejy , and relatively large and pointed in Malagasya n. gen.); by the anterolateral margins of the carapace (which are granular in Marojejy , but conspicuously toothed in Malagasya n. gen.); and by the frontal region (which is wide and moderately deflexed in Marojejy , but narrow and sharply deflexed in Malagasya n. gen.).

Malagasya n. gen. can be distinguished from Skelosophusa as follows: Malagasya n. gen. has an elongated, heart-shaped carapace outline, narrow frontal and posterior carapace margins, a sharply pointed epibranchial tooth, several small teeth on the anterolateral margin, and a sharply deflexed vertical front. In contrast, Skelosophusa has a transversely oval carapace, relatively wide frontal and posterior margins of the carapace, a blunt and low epibranchial tooth, smooth or granular (never toothed) anterolateral margins, and a moderately deflexed (not vertical) front.