Chinapotamon halangense, Do & Tan & Nguyen, 2025

Chinapotamon halangense sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3

Chinapotamon cf. depressum View in CoL – Le et al. 2024: 504–507, figs 2, 3, 10 A. (not Tiwaripotamon depressum Dai, Song, Li & Liang, 1980 View in CoL )

Material examined.

Holotype • 1 male (34.9 × 26.8 mm) ( IB - FC-CHx 01), a small stream in Lung Roi , Coong Hoai Village, Duc Quang Commune, Ha Lang District, Cao Bang Province, Vietnam, 22°43'25.2"N, 106°40'29.3"E, 14 May 2019, Do et al. leg GoogleMaps . Paratypes • 2 males (34.4 × 26.3 mm, 32.5 × 25.2 mm), 1 female (27.2 × 21.3 mm) ( ZRC 2024.0312 View Materials ), same data as holotype GoogleMaps • 1 male (31.5 × 24.8 mm), 1 female (33.9 × 26.6 mm) ( IB - FC-CHx 03), a small stream in Lung Roi , Coong Hoai Village, Duc Quang Commune, Ha Lang District, Cao Bang Province, Vietnam, 22°43'25.2"N, 106°40'29.3"E, 15 May 2019, Do et al. leg GoogleMaps . • 1 male (31.1 × 24.9 mm), 1 female (27.8 × 21.8 mm) ( IB - FC-CHx 04) a small stream in Khau Noc , Coong Hoai Village, Duc Quang Commune, Ha Lang District, Cao Bang Province, Vietnam, 22°43'46.6"N, 106°40'09.3"E, 15 May 2019, Do et al. leg GoogleMaps . • 1 male (27.9 × 21.5 mm), 1 female (33.8 × 26.2 mm) ( IB - FC-CHx 05), a small stream, Coong Hoai Village , Duc Quang Commune, Ha Lang District, Cao Bang Province, Vietnam, 22°42'45.8"N, 106°39'53.8"E, 15 May 2019, Do et al. leg GoogleMaps .

Diagnosis.

Carapace (Fig. 1 A View Figure 1 ) slightly wider than long, subovate (average adult carapace width 27.2–34.9 mm); dorsal surface relatively smooth, gently convex, regions not distinct. Epigastric and postorbital cristae distinct, separated by shallow groove. External orbital tooth very low. Epibranchial tooth very low, small. Cleft between external orbital and epibranchial teeth deep. Anterolateral margin of carapace slightly convex, cristate, granular; posterior margin converging strongly towards posterior carapace margin. Exopod of third maxilliped reaching to 0.3 times length of merus with flagellum shorter than width of merus (Fig. 1 D View Figure 1 ). Male major chela oblate wide gape when closed (Fig. 1 E View Figure 1 ). Ambulatory legs relatively slender; length to width ratio of last ambulatory merus = 2.5 (Fig. 1 A View Figure 1 ). Thoracic sternites 3 and 4 without trace of groove demarcating suture (Fig. 2 A View Figure 2 ). Male telson relatively broad, lateral margins slightly convex (Fig. 2 A View Figure 2 ). Subterminal article of male first gonopod slender, sinous, proximal half trapezoidal, slightly wider than distal half, gently tapering distally; terminal article slender, bent outwards at about 45 ° (Fig. 3 View Figure 3 ).

Description of holotype.

Carapace subovate, slightly wider than long, ratio CW: CL = 1.3; dorsal surface smooth, finely pitted, gently convex transversely, convex antero-posteriorly, regions poorly defined (Fig. 1 A View Figure 1 ). Frontal region smooth; lateral parts of anterolateral and branchial regions covered with short striae and small flattened granules; mesogastric, urogastric, cardiac and intestinal regions finely punctuated, otherwise smooth; orbital regions smooth; suborbital and pterygostomial regions uneven to almost smooth (Fig. 1 A, B View Figure 1 ). Epigastric cristae distinct, not sharp, separated by broad, shallow Y-shaped furrow, separated from postorbital cristae by short, shallow groove; postorbital cristae low (Fig. 1 A View Figure 1 ). Cervical grooves shallow but distinct; H-shaped median gastric groove shallow but distinct (Fig. 1 A View Figure 1 ). Frontal margin divided into 2 broad, low lobes, separated by broad, very shallow concavity; margin of each lobe gently convex, confluent with supraorbital margin (Fig. 1 A View Figure 1 ). External orbital tooth very low, demarcated from rest of anterolateral margin by small, shallow notch, lined with very low granules; epibranchial tooth very low, small, barely discernible (Fig. 1 A View Figure 1 ). Anterolateral margins distinctly cristate, lined with granules (Fig. 1 A View Figure 1 ). Posterolateral margin strongly converging towards posterior carapace margin (Fig. 1 A View Figure 1 ). Orbits subovate; eye filling orbit; ocular peduncle long; cornea normal (Fig. 1 B View Figure 1 ). Supraorbital margin weakly concave, entire, lined with small, flattened granules (Fig. 1 B View Figure 1 ). Suborbital margin concave, complete, lined with small granules (Fig. 1 B View Figure 1 ). Posterior margin of epistome with distinct broad median triangle, each lateral margin with 2 lateral concavities (Fig. 1 C View Figure 1 ).

Ischium of third maxilliped subrectangular, about 1.4 times longer than broad, smooth, with distinct median oblique groove; merus subquadrate, about 0.8 times as long as broad, surface smooth, anteroexternal angle broadly triangular, not expanded; exopod slender, reaching to 0.3 times length of merus, flagellum distinct, shorter than width of merus (Fig. 1 D View Figure 1 ).

Male chelipeds asymmetrical in size (Fig. 1 A, E View Figure 1 ). Anterior margin of basis-ischium almost smooth; inner-lower margins of merus granulated (Fig. 1 E View Figure 1 ). Outer surface of carpus gently rugose, inner distal angle with distinct sharp tooth, with 2 smaller teeth basally (Fig. 1 A View Figure 1 ). Outer surfaces of chelae with numerous pits, otherwise smooth; chela palm in large males approximately 1.3 times as long as broad; major chela stouter, longer than minor chela (Fig. 1 E View Figure 1 ). Fingers of major chela, stout, curved, shorter than palm, outer surface lined with 2 rows of pits; cutting edges of both fingers with stout teeth, forming slight gape when closed, with tips not crossing (Fig. 1 E View Figure 1 ). Fingers of minor chela slender, shorter than major chela, fingers relative straight, with small gape when closed (Fig. 1 E View Figure 1 ).

Ambulatory legs not elongated, slender; second pair longest, last pair shortest (Fig. 1 A View Figure 1 ). Outer surface of merus slightly rugose, dorsal margin weakly serrated, length to width ratio of fourth merus = 3.4, and for propodus = 2.3; carpus slightly rugose, outer surface with submedian crista on first to third legs; propodus subrectangular, length to width ratio of fourth propodus = 2.3; dactylus gently curved, margins with short, sharp pectinate spines on both inner and outer margins (Fig. 1 A View Figure 1 ).

Thoracic sternites relatively broad transversely (Fig. 2 A View Figure 2 ). Sternites 1, 2 completely fused to form broadly triangular plate; separated from sternite 3 by complete suture; sternites 3, 4 completely fused, without a trace of groove demarcating suture; sternopleonal cavity reaching to imaginary line connecting bases of cheliped coxae (Fig. 2 B View Figure 2 ). Male pleonal locking tubercle just aft of median part of sternite 5 (Fig. 2 B View Figure 2 ). Male pleon triangular; telson relatively broad with lateral margins slightly convex, width to length ratio = 1.3; somite 6 broadly rectangular, width to length ratio = 1.9 (Fig. 2 A View Figure 2 ).

G 1 slender, reaching to suture between sternites 4 and 5 with terminal and subterminal articles clearly demarcated; subterminal articles relatively slender, sinuous, proximal half trapezoidal, slightly wider than distal half, tapering gently distally, directed inward proximally but outward distally, 2.6 times as long as terminal article; terminal article slender, relatively gradually tapering, bent at about 45 ° outwards, gently curving upwards, slightly upcurved distally, tip appears truncated with smaller protrusion, with groove for G 2 visible in ventral orientation (Fig. 3 View Figure 3 ). G 2 longer than G 1, distal article long, ratio of basal article to distal article = 2.6.

Females. Females are similar to male in most non-sexual features, chelipeds tend to be less asymmetrical. Female pleon ovate in mature individuals, covering thoracic sternites (Fig. 2 C View Figure 2 ). Vulvae set relatively far apart, large, almost round; directed ventral-mesially, positioned on proximal half of sternite 6, pressing against suture with sternite 5 (Fig. 2 D View Figure 2 ).

Colouration.

Dorsal surfaces orangish-brown; ventral surface white; outer and inner surfaces of chelae light purple, inner surface very light purple (cf. Le et al. 2024: fig. 10 A).

Etymology.

The new species is named after the type locality, Ha Lang District.

Distribution.

So far, this species has only been collected from Duc Quang Commune, Ha Lang District, Cao Bang Province, Vietnam. Its occurrence in small streams within well-vegetated and undisturbed forests suggests that it is possibly susceptible to anthropogenically-driven habitat disturbances.

Notes on ecology.

The new species live in limestone mountain areas, in small springs, even in stagnant pools, often with decomposing leaves, branches and humus substrate (Fig. 4 View Figure 4 ).

Remarks.

Chinapotamon halangense sp. nov. can be distinguished from all other Chinapotamon species by the combination of the following characters: (1) medium sized species ( CW of mature individuals range between 27.2–34.9 mm); (2) carapace subovate, dorsal surface convex, relatively smooth; (3) distinct epigastric and postfrontal cristae; (4) deep cleft between external orbital and epibranchial teeth; (5) anterolateral margins with distinct cristae; (6) anterolateral region gently rugose; (7) concavity between frontal margin lobes broad and shallow; (8) male major chela with oblate wide gap when closed; (9) ambulatory legs relatively slender; (10) sternites 3 and 4 completely fused, without a trace of groove demarcating suture; (11) subterminal article of male first gonopod is relatively slender, proximal half trapezoidal, distal half gently tapering distally; and (12) terminal article slender, bent outwards at about 25 °, slightly upcurved distally.

Among described species of Chinapotamon , C. depressum ( Dai, Song, Li & Liang, 1980) is morphologically closest to C. halangense sp. nov. In fact, C. halangense sp. nov. was previously referred to C. cf. depressum by Le et al., 2024, with references to the descriptions and illustrations by Dai and Naiyanetr (1994) and Dai (1999). The species shares affinities with C. depressum sensu stricto, in terms of medium adult carapace size, the relatively broad G 1 subterminal article and the G 1 terminal article being similarly bent outwards at about 25 ° (cf. Dai et al. 1980: fig. 3; Dai 1999: fig. 43). Recent photographs of the holotype specimen of C. depressum in CAS have, however, revealed some discrepancies in the G 1 morphology, when compared to the illustrations in Dai et al. (1980) and Dai (1999). Upon close examination, the new species can be distinguished from C. depressum by the following consistent differences: (1) subovate and smooth carapace (Fig. 1 A View Figure 1 ) (vs. carapace subquadrate and comparatively rugose, particularly around branchial regions, cf. Fig. 5 A View Figure 5 ); (2) epigastric and postorbital cristae faint (Fig. 1 A View Figure 1 ) (vs. well-developed epigastric and postorbital cristae, cf. Fig. 5 View Figure 5 ); (3) external orbital tooth positioned lower than frontal margin (Fig. 1 A View Figure 1 ) (vs. external orbital tooth positioned higher than frontal margin, cf. Fig. 5 View Figure 5 ); (4) suture separating sternites 3 and 4 barely visible (Fig. 1 A View Figure 1 ) (vs. suture separating sternites 3 and 4 prominent, cf. Fig. 5 View Figure 5 ); (5) ambulatory legs slenderer, merus and propodus of last ambulatory leg 3.5 and 2.3 times as long as wide respectively (Fig. 1 A View Figure 1 ) (vs. ambulatory legs stouter, merus and propodus of last ambulatory 3.3 and 2.1 times as long as wide, respectively, cf. Fig. 5 View Figure 5 ; Dai 1999; Ng 2017: table 1; Zou et al. 2018: table 2); (6) major chela fingers forming large ovate gape when closed (Fig. 1 E View Figure 1 ) (vs. major chela fingers forming no gape when closed, cf. Fig. 5 View Figure 5 ; Dai 1999: pl. 4, fig. 5; cf. Zou et al. 2018: table 2); (7) telson broadly triangular, lateral margins slightly convex (Fig. 2 A View Figure 2 ) (vs. telson acutely triangular, lateral margins straight, cf. Fig. 5 View Figure 5 ); and (8) G 1 subterminal article basal part proportionally longer, with shorter, broader neck-like distal half (Fig. 3 View Figure 3 ) (vs. G 1 subterminal article basal part proportionally shorter, to proximal third of article, with longer, more slender distal neck-like part, cf. Fig. 5 D, E View Figure 5 ).