Indochinamon frontatum, Shi & Pan & Sun, 2023

Shi, Boyang, Pan, Da & Sun, Hongying, 2023, On a new species of freshwater crab from southern China (Crustacea, Brachyura, Potamidae), Zootaxa 5383 (4), pp. 575-584 : 576-582

publication ID	https://doi.org/ 10.11646/zootaxa.5383.4.8
publication LSID	lsid:zoobank.org:pub:44C52311-762B-46A0-8CC5-D7E998489E86
DOI	https://doi.org/10.5281/zenodo.10369872
persistent identifier	https://treatment.plazi.org/id/03A9851C-FFE4-3675-FF6C-02CCDCE1D174
treatment provided by	Plazi
scientific name	Indochinamon frontatum
status	sp. nov.

Treatment

Indochinamon frontatum sp. nov.

( Figs. 2–6 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Material examined. Holotype: male, 40.5 × 31.6 mm (voucher: NNU16-7472-01), 23.34°N 105.54°E, Anliang Village , Tianpeng Town , Funing County, Wenshan Zhuangzu and Miaozu Autonomous Prefecture, Yunnan Province, China, alt. 986 m, coll. Boyang Shi, Ruxiao Wang, and Hongying Sun, 24 October 2020 GoogleMaps . Paratypes: 4 males, 38.3 × 30.3 mm (voucher: NNU16-7472-02), 35.1 × 30.3 mm (voucher: NNU16-7472-03), 34.5 × 29.8 mm (voucher: NNU16-7472-04), 32.2 × 27.4 mm (voucher: NNU16-7472-05); 1 female, 39.2 × 30.6 mm (voucher: NNU 16-7472- 06); same data as holotype GoogleMaps .

Diagnosis. Carapace broader than long, dorsal surface gently convex, rugose, punctate, sparsely setose, regions distinct ( Fig. 2A View FIGURE 2 ); frontal region broad, with prominently cristae in median position ( Fig. 2A, B View FIGURE 2 ); lateral parts of anterolateral and branchial regions with oblique striae ( Fig. 2A View FIGURE 2 ); external orbital tooth distinct, separated from anterolateral margin by V-shaped cleft; epibranchial tooth prominent ( Fig. 2A View FIGURE 2 ); anterolateral margin lined with sharp granules, appears serrated ( Fig. 2A View FIGURE 2 ). Posterior margin of epistome with distinct median triangle ( Fig. 2B View FIGURE 2 ). Male pleon triangular, lateral margin of sixth somite slightly convex; telson triangular, with slightly concave lateral margin, tip rounded ( Fig. 2C View FIGURE 2 ). Chelipeds asymmetrical ( Fig. 2A View FIGURE 2 ); margins of merus lined with small sharp granules, appears weakly serrated ( Fig. 3C View FIGURE 3 ). G1 slender, distinctly sinuous ( Fig. 5A, B View FIGURE 5 ); terminal segment hooked, strongly curved outward; dorsal flap with low, broadly rounded apex medial in position ( Fig. 5C, D View FIGURE 5 ); subterminal segment broad, with neck-like distal part ( Fig. 5A, B View FIGURE 5 ).

Description. Carapace subtrapezoidal, distinctly wider than long (width to length ratio 1.4); dorsal surface gently convex from frontal view, regions not prominently inflated; with very short setae sparsely scattered, otherwise appears glabrous ( Fig. 2A View FIGURE 2 ). Frontal and orbital regions broad, rugose; frontal region with prominently cristae in median position ( Fig. 2A, B View FIGURE 2 ); lateral parts of anterolateral and branchial regions covered with oblique striae; regions distinct; cervical grooves shallow, broad, connected to deep H-shaped median gastric groove ( Fig. 2A View FIGURE 2 ). Epigastric cristae distinct, rugose, separated by deep Y-shaped groove; epigastric cristae just anterior of postorbital cristae, separated by short groove; postorbital cristae distinct, margin uneven, prominently raised, oblique, outer edge relatively low ( Fig. 2A View FIGURE 2 ). Frontal margin gently sinuous. External orbital tooth distinct, broadly triangular, outer margin more than 1.5 length of inner margin, demarcated from rest of anterolateral margin by shallow V-shaped cleft; epibranchial tooth prominent, low ( Fig. 2A View FIGURE 2 ). Anterolateral margins convex, cristate, lined with granule teeth, appears serrated ( Fig. 2A View FIGURE 2 ). Posterolateral margin almost straight ( Fig. 2A View FIGURE 2 ). Orbits subovate; eye filling orbital space; eye peduncle relatively short, stout; cornea large, round, pigmented ( Fig. 2A, B View FIGURE 2 ). Supraorbital margin almost straight ( Fig. 2A, B View FIGURE 2 ). Suborbital margin straight, smooth ( Fig. 2B View FIGURE 2 ); pterygostomial, subhepatic and suborbital regions slightly granulose, sub-branchial regions smooth ( Fig. 2B, C View FIGURE 2 ). Antennae stout; antennular fossae broad, subrectangular ( Fig. 2B View FIGURE 2 ). Posterior margin of epistome with distinct median triangle, lateral margin sinuous ( Fig. 2B View FIGURE 2 ). Third maxillipeds covering most of buccal cavity when closed ( Fig. 2B View FIGURE 2 ); ischium subrectangular, with distinct median groove, surface with scattered pits and short setae ( Fig. 3A View FIGURE 3 ); merus subquadrate, slightly wider than long, surface rugose, margins cristate ( Fig. 3A View FIGURE 3 ); exopod slender, reaching to about one-third length of merus, with elongate flagellum ( Fig. 3A View FIGURE 3 ).

Chelipeds asymmetrical ( Fig. 2A–C View FIGURE 2 ). Margins of merus lined with small sharp granules, appears weakly serrated; distal part with a sharp small tooth ( Figs. 2C View FIGURE 2 , 3B View FIGURE 3 ). Outer surface of carpus rugose, inner distal angle with large sharp tooth and basal tooth ( Fig. 2A, B View FIGURE 2 ). Outer surfaces of chelae rugose, upper part rugose with granules ( Fig. 3C View FIGURE 3 ). Fingers of major chela stout, gently curved, subequal to palm, outer surface lined with 3 rows of pits; cutting edges of both fingers with variously sized sharp teeth and denticles; dorsal margin of dactylus with low tubercles and granules ( Figs. 2C View FIGURE 2 , 3C View FIGURE 3 ). Fingers of minor chela similar to major chela in form but relatively more slender ( Fig. 3C View FIGURE 3 ).

Ambulatory legs short, segments relatively stout; second pair longest, last pair shortest ( Fig. 2A, C View FIGURE 2 ). Merus stout, outer surface rugose, dorsal margin uneven, subcristate, without subdistal spine or tooth; carpus surface rugose, dorsal margin gently cristate, outer surface with low submedian crista on first to third legs, that on fourth leg smooth; dorsal margin of propodus with crista, outer surface with low, submedian crista ( Figs. 2A, C View FIGURE 2 , 3D View FIGURE 3 ); dactylus relatively short, gently curved, margins with short, sharp pectinate spines ( Fig. 3D View FIGURE 3 ).

Male thoracic sternum smooth, surface with a few pits and scattered short, stiff setae ( Fig. 4A, B View FIGURE 4 ). Sternites 1 and 2 completely fused to form broadly triangular plate; suture sternites 2 and 3 distinct; sternites 3 and 4 completely fused, with shallow incomplete groove demarcating suture near the upper lateral margins ( Fig. 4A, B View FIGURE 4 ). Male sternopleonal cavity deep, reaching imaginary line connecting posterior edges of cheliped coxae ( Fig. 4A, B View FIGURE 4 ).

Male pleonal locking tubercle low, round, on posterior third of sternite 5 ( Fig. 4B View FIGURE 4 ). Male pleon triangular, all somites and telson free; telson triangular, lateral margins gently concave; somite 6 transversely rectangular, lateral margin gently convex; somites 3–5 trapezoidal, gradually decreasing in width, increasing in length ( Fig. 4A View FIGURE 4 ); somites 1 and 2 subrectangular, reaching to bases of coxae of fourth ambulatory legs, thoracic sternite 8 not visible when pleon closed ( Fig. 4A View FIGURE 4 ). Female pleon ovate, covering most of thoracic sternum ( Fig. 4C View FIGURE 4 ). Vulvae on sternite 6, impinging on sutures of sternites 5 and 6, opening directed antero-mesially ( Fig. 4D View FIGURE 4 ).

G1 slender, distinctly sinuous, not reaching the pleonal locking tubercle in situ ( Figs. 4B View FIGURE 4 , 5A, B View FIGURE 5 ); terminal segment hooked, strongly curved, bent at approximately 45° outwards, about 0.3 times length of subterminal segment, about 3.2 times longer than proximal width ( Figs. 5A–D View FIGURE 5 , 6A, B View FIGURE 6 ); dorsal flap extending along proximal third to half of terminal segment, with low, broadly rounded apex medial in position ( Figs. 5A–D View FIGURE 5 , 6A, B View FIGURE 6 ); subterminal segment broad, with neck-like distal part ( Figs. 5A, B View FIGURE 5 , 6A, B View FIGURE 6 ). G2 elongate, much longer than G1; subterminal segment longer than terminal segment ( Fig. 5E View FIGURE 5 ).

Etymology. The species name is derived from an arbitrary combination of the Latin ‘frons’, alluding to its distinctive frontal region of carapace with strong cristae. Gender neuter.

Colour. In life, the dorsal surfaces of the carapace and outer surfaces of the chelipeds are greyish green, with the ventral surfaces pale yellow, and the ambulatory legs are dark brown to orangish red.

Habitat. This primarily aquatic species is found in the pools of limestone hill streams where they hide in crevices.

Remarks. The genus Indochinamon was established by Yeo & Ng (2007) for Indochinese species previously placed in Potamon Savigny, 1816 s. l., and defined by the G1 terminal segment being relatively short and stout, with the groove for the G2 marginal in position. The carapace characters are very similar in most Indochinamon species: carapace low, with relatively flat dorsal surface; epigastric cristae separated from postorbital cristae by distinct groove; and the postorbital cristae not confluent with the epibranchial tooth. However, the morphological differences of the G1 terminal segments among the species in this genus can be very significant. Thus, Ng & Win Mar (2018) separated Indochinamon into four main groups by the morphological characters of the G1 terminal segments: 1) short and stout, gently bent; 2) slender, elongate, and straight; 3) curved; and 4) strongly bent. The G1 of new species closely resembles that of the curved G1 group (group 3).

In this group, the new species is likely to be confused with I. malipoense Zhang & Sun in Zhang, Pan, Hao & Sun, 2020, as the G1 terminal segment gently bent outwards and curving. However, the new species can be distinguished by the following combination of diagnostic morphological characters: the frontal region of carapace with prominently cristae in median position just behind of frontal margin ( Fig. 2A View FIGURE 2 ) (versus the incomplete cristae or rugosity just behind the frontal margin); the G1 terminal segment is prominently hooked and bent at about 45° outward, and the dorsal flap with low, broadly rounded apex medial in position ( Figs. 5A–D View FIGURE 5 , 6A, B View FIGURE 6 ) (versus the G1 terminal segment is slightly hooked and bent at about 30° outward, and the dorsal flap with rounded apex proximal in position) (cf. Zhang, Pan, Hao & Sun 2020: I. malipoense figs. 7B, 8B, C, F, 10A). The new species is also superficially similar to I. ahkense Naruse, Chia, & Zhou, 2018 in this group, but can be further distinguished by a unique combination of the curved G1 terminal segment and the higher dorsal flap exceeding inner margin (versus the relatively straight G1 terminal segment with the lower dorsal flap not exceeding inner margin) (cf. Naruse, Chia & Zhou, 2018: I. ahkense fig. 4).

The new species is externally differentiated from the strongly curved G1 group (group 4), such as I. boshanense ( Dai & Chen, 1985) , I. flexum ( Dai, Song, Li & Liang, 1980) , and I. dangi Naruse, Nguyen & Yeo, 2011 , by the the G1 terminal segment being slender, more strongly hooked, and gently tapering distally ( Figs. 5A–D View FIGURE 5 , 6A, B View FIGURE 6 ) (versus the G1 terminal segment is stout, relatively straight, with inflated proximal part) (cf. Dai 1999: I. boshanense , fig. 96, I. flexum fig. 97; Naruse, Nguyen & Yeo, 2011: I. dangi , fig. 9d, 9e).

The new species is different from most of the congeners in having distinctly convex cristae on the frontal region, at least based on the series of six specimens on hand which includes adults and juveniles. We regard this as a diagnostic character for I. frontatum sp. nov.