Tortomon gejiu, 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 : 7-13

publication ID	https://doi.org/ 10.6620/ZS.2020.59-24
DOI	https://doi.org/10.5281/zenodo.8055870
persistent identifier	https://treatment.plazi.org/id/4E0587D6-FF98-2A05-FEBC-FED9E764FD82
treatment provided by	Valdenar
scientific name	Tortomon gejiu
status	gen. nov.

Treatment

Tortomon gejiu View in CoL View at ENA n. gen. n. sp.

( Figs. 4–6 View Fig View Fig View Fig , 7C, D View Fig , 8B View Fig ) urn:lsid:zoobank.org:act:D7161B21-695D-4094-B1E7-4A168460C585

Material examined: Holotype: SYSBM 001834 , male (20.1 × 14.0 mm), Yangjiatian Village (23.33°N, 103.15°E), Gejiu City, Honghe Hani and Yi Autonomous Prefecture , Yunnan, China, small hillstream, 1,800 m a.s.l., coll. J. Wang, May, 2018 GoogleMaps . Paratypes: SYSBM 001246-001248, 3 males (23.7 × 16.4 mm, 17.0 × 12.1 mm, 16.7 × 12.1 mm), Yangjiatian Village, Honghe Hani and Yi Autonomous Prefecture, Yunnan, China, small hillstream, 1800 m a.s.l., coll. M. Hou, October, 2013. SYSBM 001835, 1 female (19.1 × 14.2 mm), same data as holotype. AM P.104574, 1 male (17.6 × 13.3 mm), same data as holotype. NCHUZOOL 16430, 2 males (19.3 × 14.1 mm, 18.5 × 13.3 mm), same data as holotype.

Description: Male: Small sized (CW <24 mm). Carapace broader than long, width 1.4 times length (n = 8), regions indistinct; dorsal surface smooth, finely pitted, convex ( Fig. 4 View Fig ). Front deflexed, margin slightly ridged in dorsal view ( Fig. 4 View Fig ). Epigastric cristae and postfrontal cristae smooth, low, inconspicuous ( Fig. 4 View Fig ). Branchial regions swollen; cervical groove indiscernible; mesogastric region convex ( Fig. 4 View Fig ). External orbital tooth inconspicuous; external orbital angle fused with anterolateral margin ( Figs. 4 View Fig , 5A View Fig ). Epibranchial tooth indiscernible ( Figs. 4 View Fig , 5A View Fig ). Anterolateral margin smooth, lined with smoothly fused granules ( Figs. 4 View Fig , 5A View Fig ). Posterolateral surface smooth ( Fig. 4 View Fig ). Orbits small, supraorbital and infraorbital margins ridged, smooth ( Figs. 4 View Fig , 5A View Fig ). Sub-orbital, sub-hepatic and pterygostomial regions divided by sutures; surfaces smooth ( Fig. 5A View Fig ). Epistome median lobe broadly triangular, posterior margin almost straight ( Fig. 5A View Fig ).

Maxilliped 3 merus width about 1.3 times length; ischium width about 0.7 times length; merus subtrapezoidal with median depression; ischium subtrapezoidal, with distinct median sulcus, mesial margin rounded; exopod strongly tapering, reaching to proximal quarter of merus height, flagellum absent ( Fig. 6A View Fig ).

Chelipeds unequal ( Figs. 4 View Fig , 6F–G View Fig ). Merus trigonal in cross section, surfaces and margins smooth ( Figs. 4 View Fig , 5A View Fig ). Carpus with blunt spine at inner-distal angle, spinule at base barely discernible, surfaces smooth ( Fig. 4 View Fig ). Major cheliped palm length about 1.2–1.3 times height (n = 5); dactylus 1.0–1.2 times palm length (n = 5) ( Figs. 6F–G View Fig ). Palm surface smooth, pitted. Occlusal margin of fingers lined with triangular teeth of different size; small gape when closed ( Figs. 6F–G View Fig ).

Ambulatory legs (P2–5) slender, with sparse short setae. P3 merus 0.6–0.7 times carapace length (n = 6). P5 propodus 2.2–2.6 times as long as broad (n = 5), shorter than dactylus ( Fig. 4A View Fig ).

Thoracic sternum generally smooth, pitted; sternites 1–4 wide, width 1.7 times length; sternites 1, 2 fused, forming a subtriangular structure; sternites 2, 3 fused, separated by a deep transverse sulcus; sternites 3, 4 fused, with deep “v” shaped sulcus ( Fig. 5B View Fig ). Sternopleonal cavity reaching anteriorly to level of midlength of chelipeds coxae base ( Fig. 2B View Fig ); median longitudinal groove separating sternites 7, 8 deep ( Fig. 5D View Fig ). Pleonal locking tubercle positioned at mid-length of sternites 5 ( Fig. 5D View Fig ).

Pleon narrowly triangular ( Fig. 5C View Fig ). Pleonites 3–6 progressively narrower, lateral margins almost straight; pleonite 6 2.0 times as broad as long; telson 1.3 times as broad as long, with blunt apex and concave lateral margins ( Fig. 5C View Fig ).

G1 generally straight, slender, not reaching pleonal locking tubercle in situ ( Fig. 5D View Fig ). Subterminal segment 2.9–3.0 times as long as terminal segment (n = 3), inner mesial margin slightly concave, outer mesial margin slightly convex. Terminal segment short, tapering, with large rounded tip, pointed upwards ( Figs. 6C–E View Fig , 7C, D View Fig ). G2 relatively stout, subterminal segment 2.1 times as long as terminal segment; terminal segment with thin coiled tip ( Figs. 6B View Fig , 7E View Fig ).

Female: Nonsexual characters similar to males. P3 merus 0.6 times carapace length (n = 1). P5 propodus 2.4 times as long as broad (n = 1), shorter than dactylus ( Fig. 4B View Fig ). Vulva ovate, with relatively wide space between one another; medium-sized, mainly situated on sternite 6, reaching to sternite 5 but not sternite 7 ( Fig. 5F View Fig ). Pleon broadly ovate ( Fig. 5E View Fig ).

Etymology: The new species is named as a noun after the type locality, which is in Gejiu City , Yunnan. See the Supplementary Material for its proposed Chinese name.

Colour in life: Dorsal surface generally light brown to light turquoise ( Fig. 8B View Fig ).

Habitat: This species was collected from a small hillstream at around 1,800 m a.s.l. Not much is known about its habits other than that it tends to be more active at night and can be found amongst aquatic plants. They were found in low densities at the type locality, which may be the result of the agricultural land use at the banks of the hillstream. It is possible that this species is also a semi-terrestrial burrower like its congener (see above) and the few specimens we found originated from a source population in the undisturbed environment further upstream.

Remarks: See remarks for Tortomon puer n. sp.

Phylogenetic Analysis

The molecular analysis of the 16S gene (505 bps after removing the variable regions) yielded 51 species in the Potamiscinae ( Fig. 9 View Fig ). The five specimens of Tortomon formed three subclades within a larger clade corresponding to the new genus. The three subclades correspond well with T. gejiu , T. puer and T. sp., with the former two being sister species with weak support from both BI and ME methods. Although the new genus is closest to Parapotamon De Man, 1907 in the tree, the support values are too low to suggest this. The new clade formed by Tortomon is named “SW China 2” to discriminate it from the “SW China ” clade in Shih et al. (2009).

The pairwise nucleotide divergences and differences in the total bp numbers (gaps considered), for the 520-bp 16S segment are shown in table 1. The genetic distances (and number of differences) among T. gejiu , T. puer and T. sp. are from 3.78% (19 bp) to 5.63% (30 bp).