Tortomon, Ng & Tri, 2023

Huang, Chao, Wang, Jian & Shih, Hsi-Te, 2020, A New Genus and Two New Species of Freshwater Crab (Crustacea: Brachyura: Potamidae) with Unusual Coiled Tip of Male Second Gonopods from Yunnan, Southwestern China, Zoological Studies 59 (24), pp. 1-14 : 2-3

publication ID	https://doi.org/ 10.6620/ZS.2020.59-24
DOI	https://doi.org/10.5281/zenodo.8055866
persistent identifier	https://treatment.plazi.org/id/4E0587D6-FF9F-2A0D-FC59-F9D8E3E0FEE2
treatment provided by	Valdenar
scientific name	Tortomon
status	gen. nov.

Treatment

Genus Tortomon View in CoL View at ENA n. gen.

( Figs. 1–8 View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig ) urn:lsid:zoobank.org:act:06743881-BA7C-4DB9-9AC1-D7E5E55D79FE

Type species: Tortomon puer View in CoL n. gen. n. sp., by current designation.

Diagnosis. Small sized (CW <25 mm). Carapace broader than long, smooth all over, convex; regions indistinct ( Figs. 1 View Fig , 4 View Fig ); epigastric cristae and postfrontal cristae smooth, low, inconspicuous ( Figs. 1 View Fig , 4 View Fig ); external orbital tooth inconspicuous; external orbital angle fused with anterolateral margin ( Figs. 1 View Fig , 2A View Fig , 4 View Fig , 5A View Fig ). Anterolateral margin smooth to weakly cristate ( Figs. 1 View Fig , 4 View Fig ). Orbits small ( Figs. 1 View Fig , 2A View Fig , 4 View Fig , 5A View Fig ). Median lobe of epistome broadly triangular ( Figs. 2A View Fig , 5A View Fig ). Maxilliped 3 with relatively broad ischium, exopod strongly tapering, reaching beyond anterior edge of ischium, flagellum absent ( Figs. 3A View Fig , 6A View Fig ). Cheliped merus margins smooth, palm surface smooth ( Figs. 1 View Fig , 3F–G View Fig , 4 View Fig , 6F–G View Fig ). Ambulatory legs slender ( Figs. 1 View Fig , 4 View Fig ). Male anterior thoracic sternum relatively wide, width around 1.7 times length ( Figs. 2B View Fig , 5B View Fig ). Male pleon narrowly triangular, telson with blunt apex and concave lateral margins ( Figs. 2C View Fig , 5C View Fig ). G1 generally straight and slender; terminal segment short, tapering, with blunt tip; pointing upwards to slightly bent outwards ( Figs. 3C–E View Fig , 6C–E View Fig , 7A–D View Fig ). G2 terminal segment short, with thin coiled tip ( Fig. 3B View Fig , 6B View Fig , 7E View Fig ). Female vulva with relatively wide space between one another, ovate; medium-sized, mainly situated on sternite 6, reaching to sternite 5 but not sternite 7 ( Figs. 2F View Fig , 5F View Fig ). Female pleon ovate ( Figs. 2E View Fig , 5E View Fig ).

Etymology: The genus name is an arbitrary combination of Latin tortus and the type genus of Potamidae , Potamon . It alludes to the coiled tip of the G2 of the new genus, which is its most distinctive character. Gender: neuter. See the Supplementary Material for its proposed Chinese name.

Distribution: Yunnan, China.

Remarks: Tortomon n. gen. is included in the Potamiscinae due to the absence of a transverse ridge on the eighth thoracic sternite ( Yeo and Ng 2003). Its distribution in southern Yunnan also fits that of Potamiscinae , which occurs in East Asia and Southeast Asia (Yeo and Ng 2004). The new genus is quite unique, with only Tenuipotamon Dai, 1990 and Parvuspotamon Dai & Bo, 1994 being comparable to it within the Potamidae . Most notably, the coiled tip of the G2 terminal segment is a rare character in brachyurans (see DISCUSSION) and is not seen in any other known potamid. It is closest to Tenuipotamon in morphology, but differs in its narrowly triangular male pleon ( Figs. 2C View Fig , 5C View Fig ) (versus widely triangular in Tenuipotamon ; Dai, 1999: fig. 205 (2)), G1 terminal segment that points upwards to slightly bent outwards ( Figs. 3C–E View Fig , 6C–E View Fig , 7A–D View Fig ) (versus bent inwards in Tenuipotamon ; Dai, 1999: fig. 205 (5)), and G2 terminal with a thin coiled tip ( Fig. 3B View Fig , 6B View Fig , 7E View Fig ) (versus tip without this structure in Tenuipotamon ; Dai, 1999: fig. 205 (6)). Tortomon n. gen. is also similar to Parvuspotamon , but differs in that its external orbital angle is fused with anterolateral margin ( Figs. 1 View Fig , 4 View Fig ) (versus separated by narrow gap in Parvuspotamon ; Naruse et al. 2018: fig. 24B), small orbits ( Figs. 2A View Fig , 5A View Fig ) (versus larger orbits in Parvuspotamon ; Naruse et al. 2018: fig. 24), anterior thoracic sternum relatively wide, width around 1.7 times the length, sternite 2 relatively small ( Figs. 2B View Fig , 5B View Fig ) (versus relatively narrow, width around 1.5 times the length, sternite 2 relatively large in Parvuspotamon ; Naruse et al. 2018: fig. 25), male telson lateral margins concave ( Figs. 2C View Fig , 5C View Fig ) (versus slightly convex in Parvuspotamon ; Naruse et al. 2018: fig. 25A), G1 terminal segment short ( Figs. 3C–E View Fig , 6C–E View Fig , 7A–D View Fig ) (versus slender and long in Parvuspotamon ; Dai, 1999: fig. 216(4)), and the G2 terminal segment with a thin coiled tip ( Figs. 3B View Fig , 6B View Fig , 7E View Fig ) (versus tip without this structure in Parvuspotamon ; Dai, 1999: fig. 205 (6)).