Eosamon daiae Zhang & Sun, 2020

Zhang, Zewei, Pan, Da, Hao, Xiyang & Sun, Hongying, 2020, Two new species of freshwater crabs of the genera Eosamon Yeo & Ng, 2007 and Indochinamon Yeo & Ng, 2007 (Crustacea, Brachyura, Potamidae) from southern Yunnan, China, ZooKeys 980, pp. 1-21 : 1

publication ID	https://dx.doi.org/10.3897/zookeys.980.52186
publication LSID	lsid:zoobank.org:pub:A72A4909-3C62-4176-9B29-CE9BA22A9923
persistent identifier	https://treatment.plazi.org/id/3753C63F-4E88-4650-AC9D-D21A2A8880B7
taxon LSID	lsid:zoobank.org:act:3753C63F-4E88-4650-AC9D-D21A2A8880B7
treatment provided by	ZooKeys by Pensoft
scientific name	Eosamon daiae Zhang & Sun
status	sp. nov.

Treatment

Eosamon daiae Zhang & Sun View in CoL sp. nov. Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6

Material examined.

Holotype: China • 1 male, 26.6 × 22.2 mm, NNU 190503; Yunnan Province, Dehong Prefecture, Longchuan County, Longba Town, Bangyang Village; 24°18'15"N, 97°47'56"E; 998 m a.s.l.; 5 May 2019; leg. Xiyang Hao & Zewei Zhang. Paratypes: China • 1 female, 20.1 × 16.5 mm, NNU 190505; same data as holotype • 1 male, 24.8 × 20.4 mm, NNU 190504; same data as holotype. Other material: China • 3 males, 20.9 × 17.5 mm, NNU 190401, 23.0 × 19.3 mm, NNU 190402, 21.5 × 17.8 mm, NNU 190403; same data as holotype. CHINA • 1 female, 19.7 × 16.5 mm, NNU 190407; Yunnan Province, Ruili City, Nongdao Town, Dengga Village; 23°55'51"N, 97°47'56"E; 887 m a.s.l.; 4 May 2019, leg. Xiyang Hao & Zewei Zhang.

Comparative material.

Eosamon tumidum (Wood-Mason, 1871): China • 1 male, 23.2 × 18.7 mm, IZCAS CB11382; Yunnan Province, Sipaishan; 1964; Eosamon tengchongense (Dai & Chen, 1985): China • 1 male, 37.9 × 30.1 mm, NNU 193261; Yunnan Province, Lianghe County; 9 May 2019; leg. Xiyang Hao & Zewei Zhang; Eosamon lushuiense (Dai & Chen, 1985): China • 1 male, 23.7 × 19.9 mm, NNU 162821; Yunnan Province, Lushui City; 4 May 2016; leg. Kelin Chu, Pengfei Wang & Hongying Sun.

Diagnosis.

Carapace slightly broader than long, dorsal surface strongly convex, densely pitted (Fig. 2A View Figure 2 ). Third maxilliped exopod reaching proximal 1/3 of merus length, with long flagellum (Fig. 3A View Figure 3 ). Male pleon triangular, lateral margin almost straight (Fig. 2C View Figure 2 ), G1 subterminal segment broad, terminal segment relatively short, clearly sinuous, inferior margin of terminal segment straighter than superior margin, tip of terminal segment gradually tapering to a sharp tip (Fig. 3F View Figure 3 ), subterminal segment about 3.3 times as long as terminal segment (Fig. 3B, C View Figure 3 ). G1 strongly curved outwards, not reaching pleonal locking mechanism in situ (Fig. 3E View Figure 3 ). Female pleon ovate (Fig. 4A View Figure 4 ), vulvae on suture between thoracic sternites 5/6, ovate, opening inner upwards, vulvar cover margin slightly arched (Fig. 4B View Figure 4 ).

Description.

Carapace about 1.2 times broader than long (N = 6), subquadrate, dorsal surface strongly convex transversely and longitudinally, punctate, smooth, regions distinctly defined (Fig. 2A View Figure 2 ); anterolateral region lined with granules; posterolateral margin with rugae (Fig. 2A View Figure 2 ); cervical groove and H-shaped groove between gastric and cardiac regions deep, distinct (Fig. 2A View Figure 2 ). Epigastric region distinct, separated by narrow groove (Fig. 2A View Figure 2 ). Postfrontal lobe slightly convex, separated medially by Y-shaped groove extending to frontal region (Fig. 2A View Figure 2 ). Front deflexed downwards, postorbital region distinctly concave (Fig. 2A, B View Figure 2 ). Dorsal orbital margin ridged, external orbital angle triangular, epibranchial tooth pointed, clearly demarcated from external orbital tooth by gap; supraorbital and infraorbital margins cristate (Fig. 2A, B View Figure 2 ). Branchial regions relatively flat, smooth with dense dots (Fig. 2A View Figure 2 ). Pterygostomial regions smooth with several granules; epistome lateral margins sinuous; median lobe triangular (Fig. 2B View Figure 2 ).

Third maxilliped merus about 1.2 times as broad as long, trapezoidal, with median depression; ischium about 1.2 times as long as broad, rectangular, with distinct median sulcus; exopod reaching proximal 1/3 of merus length with flagellum (Fig. 3A View Figure 3 ).

Chelipeds slightly unequal; merus trigonal in cross section, margins crenulated (Fig. 2A View Figure 2 ); carpus with sharp spine on inner-distal angle, with spinule at base and striae (Fig. 2A View Figure 2 ); manus of major chela with convex granules, about 1.5 times as long as high (Fig. 2A View Figure 2 ); dactylus bent inwards (Fig. 2A View Figure 2 ), gap narrow when fingers closed, cutting edge lined with irregular sized teeth (Fig. 2A View Figure 2 ).

Ambulatory legs relatively stout, dactylus slender with spine-like setae (Fig. 2A View Figure 2 ); second ambulatory leg merus about 1.3 times as long as dactylus; last leg with propodus about 1.7 times as long as broad, slightly shorter than dactylus (Fig. 2A View Figure 2 ).

Male thoracic sternum generally smooth and pitted; sternites 3, 4 fused without median suture (Fig. 2C View Figure 2 ). Female thoracic sternum wider, sutures the same as male.

Male pleon triangular, third somite widest; sixth somite about 2.2 times broader than long; telson triangular, with about 1.3 times as broad as long; the lateral margin of pleon almost straight (Fig. 2C View Figure 2 ); sterno-pleonal cavity reaching anteriorly to level of mid-length of cheliped coxae bases, broad, deep, median longitudinal groove between sternites 7, 8 long (Fig. 3E View Figure 3 ). Female pleon ovate, surface pitted; sixth somite about 2.8 times as broad as long; telson semicircular, terminal gently protuberant, about 2.3 times as broad as long (Fig. 4A View Figure 4 ).

G1 stout, tip of terminal segment not reaching pleonal locking mechanism in situ (Fig. 3E View Figure 3 ); subterminal segment stout, about 3.3 times as long as terminal segment (Fig. 3B, C View Figure 3 ); G1 terminal segment cone-shape, bent outwards, inferior margin of terminal segment straighter than superior margin, tip of G1 terminal segment gradually tapering to sharp tip (Fig. 3F View Figure 3 ). G2 slightly longer than G1, basal segment about 2.1 times as long as distal segment (Fig. 3D View Figure 3 ). Female vulvae on suture between thoracic sternites 5/6, ovate, opening inwards towards the median of the cavity, vulvar cover slightly arched (Fig. 4B View Figure 4 ).

Live coloration.

Carapace is usually dark brown, while chelipeds and ambulatory legs are usually light brown in life.

Etymology.

The species is named after the late Prof. Aiyun Dai, who made a huge contribution to freshwater crab studies in China during her lifetime.

Remarks.

Eosamon daiae sp. nov. can be distinguished from other Eosamon species by the combination of male abdomen with straight lateral margins, relatively broad G1 subterminal segment, conical and straight G1 terminal segment, the superior margin of G1 terminal segment curved and the inferior margin of G1 terminal segment comparatively straight.

Eosamon daiae sp. nov. is morphologically and geographically closest to E. tumidum (Wood-Mason, 1871), E. tengchongense (Dai & Chen, 1985) and E. lushuiense (Dai & Chen, 1985). These species are characterized by a male abdomen with straight lateral margins and superficially similar G1 structure (Fig. 5 View Figure 5 ). But Eosamon daiae sp. nov. can be distinguished by the fact that the superior margin of G1 terminal segment is curved and the inferior margin is comparatively straight (Fig. 3F View Figure 3 , 5A View Figure 5 ) (versus superior margin comparatively straight and inferior margin slightly curved in both E. tumidum and E. lushuiense , Fig. 5B, C View Figure 5 ; outer and inner margins all comparatively curved in E. tengchongense , Fig. 5D View Figure 5 ); the distal part of G1 subterminal segment slightly sunken (Fig. 5A View Figure 5 ) (versus barely sunken in E. tumidum , Fig. 5B View Figure 5 , prominently sunken in E. tengchongense , Fig. 5D View Figure 5 ). Other characters as shown in Table 2 View Table 2 .

Distribution and habitat.

Eosamon daiae sp. nov. was found in Bangyang Village (24°18'15"N, 97°47'56"E, 998 m a.s.l.), Longba Town, Longchuan County and Dengga Village (23°55'51"N, 97°47'56"E, 887 m a.s.l.), Nongdao Town, Ruili City, Dehong Prefecture in the frontier of Yunnan, China (Fig. 1 View Figure 1 ). They reside in moist mud burrows on the ridge of field and under low bushes (Fig. 6 View Figure 6 ).

The new species was found not distant from localities with E. tengchongense . Indochinamon dominates the areas surrounding the new species, with I. edwardsi , I. andersonianum , I. boshanense and I. gengmaense having been recorded.