Migmathelphusa, Ng, 2006

Ng, Oliver K. S. Chia Peter K. L., 2006, The Freshwater Crabs Of Sulawesi, With Descriptions Of Two New Genera And Four New Species (Crustacea: Decapoda: Brachyura: Parathelphusidae), Raffles Bulletin of Zoology 54 (2), pp. 381-428 : 416

Migmathelphusa , new genus

Diagnosis. – Carapace narrowly transverse to squarish, flat, regions distinct, frontal margin with distinct and well developed deeply recessed median triangle, anterolateral margin with 2 epibranchial teeth and external orbital angle; external orbital angle not reaching beyond level of frontal margin. Epigastric cristae strong, sharp, subparallel to frontal margin. Postorbital cristae weak to absent. Third maxilliped exopod with flagellum extending beyond width of merus. Chelipeds equal even in adult male specimens. Chela slender, fingers almost equal in length to palm of chela. Male abdomen distinctly T-shaped, narrow, with proximal segments broader but narrowing sharply from segments 5 onwards. Ambulatory legs long with third pair longest, propodus of last pair broad. G1 very slender, simple, terminal and subterminal segments indistinctly or cannot be demarcated, terminal segment tapered to sharp, G2 shorter than G1, with basal segment longer than well developed distal segment.

Etymology. – The genus name is derived from the Greek “Migma” which means “a mixture”, as this genus has an eclectic but distinct mix of characteristics; in combination with “ Thelphusa ”, a typical suffix to many freshwater crab genera.

Type species. – Migmathelphusa olivacea , new species, by present designation.

frontal median triangle distinct, complete, ventral sides strongly recessed. External orbital angle triangular, outer margin convex, about 2 times length of inner margin, first and second epibranchial teeth, blunt, low, acutely triangular, directed forwards, outer margins slightly truncate. Posterolateral regions lined with few oblique striae. Suture between thoracic sternites 2 and 3 incomplete, weak. Palm of chelipeds slightly inflated, subequal to pollex, pollex and dactylus lightly pigmented brown throughout length. Finger slender, subequal to palm. Ambulatory legs long, third pair longest, propodus of last pair broad. Dorsal margin of merus with slight cristae, without distinct subterminal spine. Male abdomen reaching imaginary line joining anterior edges of cheliped bases, T-shaped, segment 6 distinctly longer than segment 7; lateral margins of segment 7 gently concave; lateral margins of segment 6 subparallel, gently sinuous. G1 slender, gently curving outwards with tip directed inwards, outer margin straight, proximal part not clefted; distal part sharply tapering, curved ventrally. G2 with well developed distal segment, about 0.4 times length of basal segment.

Colour in preservative. – Deep olive-green.

Etymology. – The name alludes to the olive-green colour of the animal.

Distribution. Lake Poso, Central Sulawesi.

Remarks. – A new genus, Migmathelphusa , is established for Migmathelphusa olivacea , a new species described here. Superficially, M. olivacea resembles Parathelphusa sarasinorum in coloration, while its relatively broader last ambulatory propodus resembles that of Nautilothelphusa zimmeri . However, M. olivacea possesses a number of distinctive characteristics that warrant a new genus. Firstly, the postorbital cristae is weak or absent; and the G1 is slender and long, with the G2 possessing a short distal segment, about 0.40 times the length of the basal segment.