Glabrithelphusa Meyer, Cumberlidge & Koppin, 2014, n. gen.
Creators: name: Meyer, Kirstin S.
name: Cumberlidge, Neil
name: Koppin, Jennifer C.
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Potamonautidae
Glabrithelphusa

description: 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.
description: Published as part of Meyer, Kirstin S., Cumberlidge, Neil & Koppin, Jennifer C., 2014, A new genus and species of freshwater crab from Madagascar (Decapoda, Brachyura, Potamoidea, Potamonautidae), pp. 65-72 in Zootaxa 3884 (1) on pages 66-67, DOI: 10.11646/zootaxa.3884.1.5, http://zenodo.org/record/287450