Chinapotamon insulare, Anh & Dong & Tu, 2024

Chinapotamon insulare View in CoL sp. nov.

( Figs. 6–9 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 , 10C View FIGURE 10 )

Material examined. Holotype: 1 male (28.9 × 24.8 mm), IEBR-FC-CIx01, Vietnam, Quang Ninh Province, Van Don District, Bai Tu Long National Park, a small stream in Ba Mun Island , N 21°04’28.0” E 107°35’33.1”, coll. Do V.T. & Le H.A., 31 April 2018. GoogleMaps Paratypes: 5 males (21.4 × 18.0 mm, 23.0 × 20.0 mm, 24.5 × 21.5 mm, 25.0 ×22.0 mm, 28.0 × 23.5 mm), 3 females (22.0 × 18.0 mm, 22.6 × 18.3 mm, 26.5 × 22.0 mm), IEBR-FC-CIx02, same data as holotype. GoogleMaps Others: 2 males (23.9 × 20.5 mm, 22.3 × 18.3 mm), IEBR-FC-CIx03, Vietnam, Quang Ninh Province, Van Don District, Bai Tu Long National Park, a small stream in Ba Mun Island , N 21°04’28.0” E 107°35’33.1”, coll. Do V. T. & Le H.A., 5 June 2018 GoogleMaps ; 1 female (17.9 × 15.2 mm), IEBR-FC-CIx04, Vietnam, Quang Ninh, Van Don, Bai Tu Long National Park, a small stream in Cai Lim Island, near Cai Lim Forest Ranger Station , N 21°06’30.6” E 107°34’42.8”, coll. Do V. T., 19 March 2023 GoogleMaps ; 1 male (21.0 × 18.5 mm), IEBR-FC-CIx05, Vietnam, Quang Ninh, Van Don, Bai Tu Long National Park , Cao Lo stream in Ba Mun Island , N 21°05’00.3” E 107°35’59.0”, coll. Do V. T., 20 March 2023 GoogleMaps ; 1 male (28.9 × 24.7 mm), IEBR-FC-CIx06, Vietnam, Quang Ninh, Co To District, a small stream in Co To Island , N 21°00’34.1” E 107°44’57.8”, coll. Phan Q. T., 22 March 2023 GoogleMaps ; 1 male (19.5 × 16.0 mm), IEBR-FC-CIx07, Vietnam, Quang Ninh, Co To, a small stream in Thanh Lan Island , N 21°00’50.7” E 107°49’11.8”, coll. Phan Q. T., 23 March 2023. GoogleMaps

Description. Carapace subquadrate, about 1.2 times broader than long; dorsal surface rugose, strongly convex, regions well defined ( Figs. 6A, B View FIGURE 6 ). Frontal region rugose; lateral parts of anterolateral and branchial regions covered with small granules; mesogastric, urogastric, cardiac and intestinal regions covered with very small granules; orbital regions rugose; suborbital and pterygostomial regions, uneven, rugose covered by small granules ( Fig. 6A, B View FIGURE 6 ). Epigastric cristae low, separated by broad, shallow Y-shaped furrow, separated from postorbital cristae by short, shallow groove; postorbital cristae low, confluent with epibranchial tooth, breaking up into rugae and granules before epibranchial tooth ( Figs. 6A, B View FIGURE 6 ). Cervical grooves shallow, discernable; H-shaped median gastric groove shallow but distinct ( Fig. 6A View FIGURE 6 ). Frontal margin divided into 2 broad, high lobes, separated by broad, deep concavity; margin of each lobe gently convex, confluent with supraorbital margin ( Fig. 6A View FIGURE 6 ). External orbital tooth high, demarcated from rest of anterolateral margin by small, deep notch, lined with distinct granules; epibranchial tooth high, distinct ( Figs. 6A, B View FIGURE 6 ).

Anterolateral margins convex, strongly cristate, lined with distinct granules ( Fig. 6A View FIGURE 6 ). Posterolateral margin gently concave, strongly converging towards gently convex posterior carapace margin ( Fig. 6A View FIGURE 6 ). Orbits subovate; eye fully filling orbit; ocular peduncle long; cornea normal ( Figs. 6A, B View FIGURE 6 ). Supra- and infraorbital margin gently sinuous, lined with small but distinct granules ( Fig. 6B View FIGURE 6 ). Suborbital margin concave, complete, lined with small granules ( Fig. 6B View FIGURE 6 ). Posterior margin of epistome with distinct narrow median triangle, each lateral margin with 2 concavities ( Fig. 6B View FIGURE 6 ).

Ischium of third maxilliped subrectangular, about 1.5 times longer than broad, with distinct median oblique groove; merus subquadrate, about 0.9 times as long as broad, surface smooth, anteroexternal angle broadly triangular, not expanded; exopod slender, reaching to one-fourth length of merus, flagellum distinct, longer than width of merus ( Fig. 6C View FIGURE 6 ).

Male major chelipeds unequal, female major chelipeds more equal ( Figs. 6B, D View FIGURE 6 ). Anterior margin of basisischium almost smooth; Inner margins of merus granulated ( Figs. 6A View FIGURE 6 , 7A View FIGURE 7 ). Outer surface of carpus rugose, inner distal angle with distinct sharp tooth, with 2 smaller teeth basally ( Figs. 6A View FIGURE 6 , 7A View FIGURE 7 ). Outer surfaces of chelae rugose; chela palm in large males approximately 1.4 times as long as broad; major chela stouter, longer than minor chela ( Fig. 6D View FIGURE 6 ). Major chela with fingers stout, almost straight, shorter than palm, outer surface lined with 2 rows of pits; cutting edges of both fingers with stout teeth, almost no gap when fingers closed, not crossing ( Fig. 6D View FIGURE 6 ). Minor chela with fingers slender, shorter than major chela, two fingertips relatively straight, almost no gap when closed ( Fig. 6D View FIGURE 6 ).

Ambulatory legs not elongated; second pair longest, last pair shortest ( Fig. 6A View FIGURE 6 ). Outer surface of merus slightly rugose, dorsal margin weakly serrated, length to width ratio of fourth merus 2.1; carpus slightly rugose, outer surface with submedian crista on first to third legs; propodus subrectangular, length to width ratio of fourth propodus 1.8; dactylus gently curved, margins with short, sharp corneous spines on both inner, outer and upper margins ( Fig. 6A View FIGURE 6 ).

Thoracic sternum relatively narrow transversely ( Figs. 7A View FIGURE 7 ). Sternites 1, 2 completely fused to form broadly triangular plate; separated from sternite 3 by complete suture; sternites 3, 4 completely fused, without suture; sternopleonal cavity reaching to imaginary line connecting bases of cheliped coxae ( Fig. 7A View FIGURE 7 ). Male pleonal locking tubercle just behind median part of sternite 5 ( Fig. 7A View FIGURE 7 ). Male pleon narrow triangular; telson relatively narrow, lateral margins concave, width to length ratio 1.4; proximal margin of telson slightly wider than the distal margin of somite 6; somite 6 subrectangular, width to length ratio 1.8 ( Fig. 7A View FIGURE 7 ). Female pleon ovate, covering most of thoracic sternum ( Fig. 8A View FIGURE 8 ). Vulvae subovate; low vulvar cover on extend oblique edge of vulva ( Fig. 8B View FIGURE 8 ).

G1 slender, slightly sinuous, reaching to suture between sternites 4 and 5, with terminal and subterminal segments clearly demarcated; subterminal segment directed inward proximally but outward distally, 2.2 times as long as the terminal segment; terminal segment gradually tapering, bent at about 10°, gently curving inwards, tip subtruncate ( Figs. 7B View FIGURE 7 , 9A–D View FIGURE 9 ). G2 slightly shorter than G1, distal segment short, ratio of basal segment to distal segment 2.4 ( Figs. 7B View FIGURE 7 , 9E View FIGURE 9 ).

Live colouration. The dorsal surfaces are orangish- brown; this colour is brighter in the chelae; the ventral surfaces are white ( Fig. 10C View FIGURE 10 ).

Etymology. The name alludes to the insular occurrence of the species: it has only been found on islands so far. Chinapotamon is neuter.

Habitat. The new species lives in small streams on the islands even in the stagnant pools of springs that do not have regular water with dead leaves, branches, humus, stones, pebbles, and coarse sand substrate ( Fig. 11 View FIGURE 11 ).

Distribution. The survey results from many locations in Vietnam (unpublished data) showed that the distribution range of this species is relatively narrow, found only on five islands of Quang Ninh province (Cai Lim, Ba Mun, Tra Ban, Co To, Thanh Lan) ( Fig. 1 View FIGURE 1 ).

Remarks. Chinapotamon insulare sp. nov. is easily separated from congeners by the combination of the following characters: (1) the carapace is small in size (17.9–28.9 mm); (2) carapace is subquadrate; (3) carapace dorsal surface is strongly convex and rugose; (4) epigastric and postorbital cristae are low; (5) epibranchial tooth is high, distinct, demarcated from rest of anterolateral margin by deep notch; (6) concavity between frontal margin lobes is deep; (7) there is almost no gap when male major chela closes; (8) last ambulatory merus is stout, 2.1 times as long as wide; (9) telson is relatively narrow; (10) G1 terminal segment is slender, bent at about 10° inwards; and (11) G2 is slightly shorter than G1.

Chinapotamon insulare sp. nov. looks most similar to C. pusillum in the shape of carapace and G1. However, the new species can be distinguished by (1) the carapace size is slightly larger (12.9–19.6 mm; Figs. 6A, B View FIGURE 6 ) (vs. 17.9–28.9 mm in C. pusillum ; cf. Dai, 1999: pl. 4, fig. 4); (2) the carapace dorsal surface is strongly convex and rugose ( Figs. 6A, B View FIGURE 6 ) (vs. the carapace dorsal surface is slightly convex and rugose; cf. Dai 1999: pl. 4, fig. 4); (3) the concavity between frontal margin lobes is deeply concave ( Figs. 6A, B View FIGURE 6 ) (vs. the concavity between frontal margin lobes is shallow; cf. Dai 1999: pl. 4, fig. 4); (4) the epibranchial tooth is demarcated from rest of anterolateral margin by deep notch ( Figs. 6A, B View FIGURE 6 ) (vs. the epibranchial tooth is demarcated from rest of anterolateral margin by shallow notch; cf. Dai 1999: pl. 4, fig. 4); (5) the last ambulatory merus is slender, length is 2.1 times longer than width ( Figs. 6A, B View FIGURE 6 ) (vs. the last ambulatory merus is stouter, length is 1.6 times longer than width; cf. Dai 1999: pl. 4, fig. 4); (6) the G1 terminal bent at about 10° inwards ( Figs. 7B View FIGURE 7 , 9A–D View FIGURE 9 ) (vs. the G1 terminal bent at about 5° inwards; cf. Dai & Naiyanetr 1994: figs. 10.5, 10.6; Dai, 1999: figs. 42.5, 42.6); and (7) G2 basal segment is 2.4 times longer than distal segment ( Fig. 8E View FIGURE 8 ) (vs. 2.0 times longer; cf. Dai & Naiyanetr 1994: fig. 10.7; Dai 1999: fig. 42.7).