Glabrithelphusa, Meyer, Kirstin S., Cumberlidge, Neil & Koppin, Jennifer C., 2014

Meyer, Kirstin S., Cumberlidge, Neil & Koppin, Jennifer C., 2014, A new genus and species of freshwater crab from Madagascar (Decapoda, Brachyura, Potamoidea, Potamonautidae), Zootaxa 3884 (1), pp. 65-72 : 66-67

publication ID	https://doi.org/ 10.11646/zootaxa.3884.1.5
publication LSID	lsid:zoobank.org:pub:0DFB8B35-C265-4E96-876A-3B9BB051DF57
DOI	https://doi.org/10.5281/zenodo.6139263
persistent identifier	https://treatment.plazi.org/id/A9132D0C-FFF6-A112-25B8-DA58FE5CFEF2
treatment provided by	Plazi
scientific name	Glabrithelphusa
status	gen. nov.

Treatment

Glabrithelphusa n. gen.

( Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 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 View FIGURE 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 View FIGURE 1 A, 3A); third maxilliped with deep vertical sulcus on ischium ( Fig. 1 View FIGURE 1 C). Sternal sulcus s3/s4, faint, reduced to 2 side-notches ( Fig. 2 View FIGURE 2 F). Major cheliped with 3 unfused molars ( Fig. 1 View FIGURE 1 F). G1 terminal article with conspicuously raised lobe on superior margin, distal third of G1 subterminal segment curved outward ( Fig. 2 View FIGURE 2 A,B, 4A,B,C,D); G2 terminal segment flagellum-like, straight, no distal curve ( Fig. 2 View FIGURE 2 C, 4E). Walking legs (p2‒p5) normal length, not elongated (p5 merus/CW = 0.28) ( Fig. 3 View FIGURE 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 View FIGURE 2 D,E), a triangular abdomen ( Fig. 2 View FIGURE 2 F), and a G1 with a medium-length terminal article ( Fig. 2 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 1 A, 3A; Cumberlidge & Sternberg 2002 Fig. 2 View FIGURE 2 A-F). Glabrithelphusa n. gen. can also be distinguished from Foza and Malagasya by the smooth anterolateral margin of the carapace ( Fig. 1 View FIGURE 1 A, 3A), which has small teeth in Foza (Reed & Cumberlidge Fig. 1 View FIGURE 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 View FIGURE 1 A, 3A), versus a wide space or cleft between these teeth in both Hydrothelphusa and Marojejy ( Cumberlidge & Sternberg 2002 Fig. 1 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 1 C), but almost absent, and reduced to a short stub in Madagapotamon ( Cumberlidge & Sternberg 2002 Fig. 5H).