Tortomon Ng & Tri 2023, n. gen.
Creators: name: Huang, Chao
name: Wang, Jian
name: Shih, Hsi-Te
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Potamidae
Tortomon

description: Genus Tortomon n. gen.
(Figs. 1–8) urn:lsid:zoobank.org:act: 06743881-BA7C-4DB9-9AC1- D7E5E55D79FE
Type species: Tortomon puer 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, 4); epigastric cristae and postfrontal cristae smooth, low, inconspicuous (Figs. 1, 4); external orbital tooth inconspicuous; external orbital angle fused with anterolateral margin (Figs. 1, 2A, 4, 5A). Anterolateral margin smooth to weakly cristate (Figs. 1, 4). Orbits small (Figs. 1, 2A, 4, 5A). Median lobe of epistome broadly triangular (Figs. 2A, 5A). Maxilliped 3 with relatively broad ischium, exopod strongly tapering, reaching beyond anterior edge of ischium, flagellum absent (Figs. 3A, 6A). Cheliped merus margins smooth, palm surface smooth (Figs. 1, 3F–G, 4, 6F–G). Ambulatory legs slender (Figs. 1, 4). Male anterior thoracic sternum relatively wide, width around 1.7 times length (Figs. 2B, 5B). Male pleon narrowly triangular, telson with blunt apex and concave lateral margins (Figs. 2C, 5C). G1 generally straight and slender; terminal segment short, tapering, with blunt tip; pointing upwards to slightly bent outwards (Figs. 3C–E, 6C–E, 7A–D). G2 terminal segment short, with thin coiled tip (Fig. 3B, 6B, 7E). 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, 5F). Female pleon ovate (Figs. 2E, 5E).
© 2020 Academia Sinica, Taiwan
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, 5C) (versus widely triangular in Tenuipotamon; Dai, 1999: fig. 205 (2)), G1 terminal segment that points upwards to slightly bent outwards (Figs. 3C–E, 6C–E, 7A–D) (versus bent inwards in Tenuipotamon; Dai, 1999: fig. 205 (5)), and G2 terminal with a thin coiled tip (Fig. 3B, 6B, 7E) (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, 4) (versus separated by narrow gap in Parvuspotamon; Naruse et al. 2018: fig. 24B), small orbits (Figs. 2A, 5A) (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, 5B) (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, 5C) (versus slightly convex in Parvuspotamon; Naruse et al. 2018: fig. 25A), G1 terminal segment short (Figs. 3C–E, 6C–E, 7A–D) (versus slender and long in Parvuspotamon; Dai, 1999: fig. 216(4)), and the G2 terminal segment with a thin coiled tip (Figs. 3B, 6B, 7E) (versus tip without this structure in Parvuspotamon; Dai, 1999: fig. 205 (6)).
description: Published as part of 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, pp. 1-14 in Zoological Studies 59 (24) on pages 2-3, DOI: 10.6620/ZS.2020.59-24, http://zenodo.org/record/8069494