A new genus and species of freshwater crab from Madagascar (Decapoda, Brachyura, Potamoidea, Potamonautidae) Author Meyer, Kirstin S. Author Cumberlidge, Neil Author Koppin, Jennifer C. text Zootaxa 2014 3884 1 65 72 journal article 10.11646/zootaxa.3884.1.5 1b9a7949-14c3-4367-a7b9-b125a92597c6 1175-5326 287450 0DFB8B35-C265-4E96-876A-3B9BB051DF57 Glabrithelphusa n. gen. ( Figs. 1–4 ) Type species. Glabrithelphusa angene n. sp. , by monotypy. Etymology. The name Glabrithelphusa refers to the characteristic smooth ( glabrous in Latin) and untextured nature of the dorsal carapace of this taxon, in suite with the traditional freshwater crab genus name Thelphusa , and is a masculine noun in the singular. Diagnosis. Mandibular palp 2-segmented with small, hard, anterior lobe at junction between segments, 0.25x length of terminal segment ( Fig. 2 D,E). Entire dorsal surface of carapace smooth; cervical grooves short; suborbital region smooth; postfrontal crest faint, incomplete, epibranchial, exorbital teeth weak, low; space or cleft between epibranchial tooth and exorbital tooth reduced to small but distinct shallow notch ( Fig. 1 A, 3A); third maxilliped with deep vertical sulcus on ischium ( Fig. 1 C). Sternal sulcus s3/s4, faint, reduced to 2 side-notches ( Fig. 2 F). Major cheliped with 3 unfused molars ( Fig. 1 F). G1 terminal article with conspicuously raised lobe on superior margin, distal third of G1 subterminal segment curved outward ( Fig. 2 A,B, 4A,B,C,D); G2 terminal segment flagellum-like, straight, no distal curve ( Fig. 2 C, 4E). Walking legs (p2‒p5) normal length, not elongated (p5 merus/CW = 0.28) ( Fig. 3 A). Remarks. Glabrithelphusa n. gen. is assigned to the Potamonautidae Bott, 1970 , because of the common possession of a suite of diagnostic familial characters, including a 2-segmented mandibular palp ( Fig. 2 D,E), a triangular abdomen ( Fig. 2 F), and a G1 with a medium-length terminal article ( Fig. 2 A,B, 4A,B) ( Cumberlidge 1999 ). Glabrithelphusa can be distinguished from the other Malagasy freshwater crab genera by the form of the mandibles. Although all potamonautid crabs possess a 2-segmented mandibular palp within this family, there is a great deal of variation of mandible characters, especially among the crabs found in Madagascar ( Cumberlidge 1999 ; Cumberlidge & Sternberg 2002 ). Cumberlidge & Sternberg (2002 Fig. 4 A-L) grouped Malagasy freshwater crabs based on mandibular palp characters as follows. Taxa with a simple mandible, completely lacking a lobe of any kind at the junction between the segments ( Madagapotamon Bott, 1965 ); taxa with a small, hard ledge-like anterior lobe on the mandible about 0.1 times as long as the terminal segment ( Skelosophusa Ng & Takeda, 1994 , and Boreathelphusa Cumberlidge, 2010 ); and taxa with a clearly bilobed terminal segment with a substantial medium-sized anterior lobe about 0.5 times as long as the terminal segment ( Hydrothelphusa A. Milne-Edwards, 1872 , Marojejy Cumberlidge, Boyko, & Harvey, 2002 , Malagasya Cumberlidge & Sternberg, 2002 , and Foza Reed & Cumberlidge, 2006 ). Here we recognize a fourth kind of mandibular structure in Madagascan freshwater crabs for Glabrithelphusa n. gen. in which the mandible has a small, hard ledge-like anterior lobe about 0.25x as long as the terminal segment ( Fig. 2 D,E). Besides the mandibles, other important taxonomic characters that set Glabrithelphusa n. gen. apart from the seven other Madagascar freshwater crab genera include its completely smooth dorsal carapace surface ( Fig. 1 A, 3A; Cumberlidge & Sternberg 2002 Fig. 2 A-F). Glabrithelphusa n. gen. can also be distinguished from Foza and Malagasya by the smooth anterolateral margin of the carapace ( Fig. 1 A, 3A), which has small teeth in Foza (Reed & Cumberlidge Fig. 1 ), and conspicuous teeth in Malagasya . The new genus can be distinguished from Hydrothelphusa and Marojejy by the small notch-like space between the exorbital and epibranchial teeth in Glabrithelphusa n. gen. ( Fig. 1 A, 3A), versus a wide space or cleft between these teeth in both Hydrothelphusa and Marojejy ( Cumberlidge & Sternberg 2002 Fig. 1 A-C, 2F ). The walking legs (not elongated or slim) and eyestalks and corneas (normal length and size) of Glabrithelphusa n. gen. ( Fig. 1 A, 3A) further distinguish this genus from Marojejy whose walking legs are long, slender, and elongated, and whose eyestalks taper distally and have reduced corneas ( Cumberlidge & Sternberg 2002 Fig. 2 F, 8F ). Glabrithelphusa n. gen. is distinguished from Madagapotamon by the length of the flagellum of the exopod of the third maxilliped, which is long and well developed in Glabrithelphusa n. gen. ( Fig. 1 C), but almost absent, and reduced to a short stub in Madagapotamon ( Cumberlidge & Sternberg 2002 Fig. 5H ). Distribution. Madagascar .