On a new species of Chinapotamon Daiand Naiyanetr, 1994 and the first record of Chinapotamon pusillum (Song, 1984) and Songpotamon malipoense Shi, Pan & Sun, 2023 (Crustacea, Decapoda, Brachyura, Potamidae) from northern Vietnam

On a new species of Chinapotamon Daiand Naiyanetr, 1994 and the first record of Chinapotamon pusillum (Song, 1984) and Songpotamon malipoense Shi, Pan & Sun, 2023 (Crustacea, Decapoda, Brachyura, Potamidae) from northern Vietnam Van Tu Do1,2, Zhi Wan Tan3, Tong Cuong Nguyen1,2 1 Institute of Biology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Ha Noi, Vietnam 2 Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Ha Noi, Vietnam 3 Department of Biological Sciences, Faculty of Science, National University of Singapore, 16 Science Drive 4, Singapore 117558, Singapore https://zoobank.org/8168358C-9C64-4DF9-849A-414A73AAEC4F Corresponding author: Van Tu Do ([email protected]; [email protected]) Academic editor: M. Christodoulou ♦ Received 25 July 2025 ♦ Accepted 18 September 2025 ♦ Published 15 October 2025 Abstract The presence of freshwater crabs of the genus Chinapotamon Dai & Naiyanetr, 1994 (Potamidae) in northern Vietnam was only recently established with the description of C. cf. depressum (Dai, Song, Li & Liang, 1980) from Cao Bang Province, and C. cf. pusillum (Song, 1984) and C. insulare Le, Dang & Do, 2024, from Quang Ninh Province (Le et al. 2024). Re-examination of the specimens referring to the first two species specimens in comparison with the holotypes and original descriptions of C. depressum and C. pusillum, revealed that C. cf. depressum represents a new species, herein named C. halangense sp. nov. While C.cf. pusillum is confirmed to be C. pusillum, a recorda that represents a range extension for the latter species. Chinapotamon halangense sp. nov., can be distinguished from congeners by distinct carapace proportions and clear differences in male gonopod morphology. In addition, we report on the discovery of Songpotamon malipoense Shi, Pan & Sun, 2023, from Ha Giang Province in northern Vietnam. As a result of these recent discoveries, Vietnam’s freshwater crab fauna now comprises 65 recognized species. Key Words Biodiversity, freshwater crab, Indochina, Potamiscinae, taxonomy Introduction A number of studies have suggested that the southern provinces of China (e.g., Yunnan and Guangxi) to be the centre of diversity for freshwater crabs belonging to the family Potamidae Ortmann, 1896 (Cumberlidge et al. 2011; Shih and Ng 2011; Pan et al. 2022b), of which, most are thought to be endemic to the respective province where the species was described. Recent freshwater crab surveys in northern Vietnam, immediately south of Yunnan and Guangxi provinces have discovered species and genera of potamids that are also found in China suggesting that the freshwater crab fauna in northern Vietnam and southern China share a close biogeographic relationship (Yeo and Ng 1998; Yeo and Naruse 2008; Do et al. 2016; Ng and Ngo 2023; Ng et al. 2023; Dang et al. 2024). Until recently, the genus Chinapotamon Dai & Naiyanetr, 1994, was believed to be a Chinese endemic, with 10 known species from Guangdong, Guangxi, and Guizhou provinces in southern China: C. depressum (Dai, Song, Li & Liang, 1980) [type species]; C. anglongense Dai & Naiyanetr, 1994; C. clarkei Ng, 2017; C. dashiwei Ng, 2017; C. glabrum (Dai, Song, Li & Liang, 1980); C. longlinense Dai & Naiyanetr, 1994; C. maolanense Zou, Bai & Zhou, 2018; C. pusillum (Song, Zoosyst. Evol. 101 (4) 2025, 1995–2012|DOI 10.3897/zse.101.166629 Copyright Do, V.T. et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. zse.pensoft.net Do, V.T. et al.: A new species of Chinapotamon and two new freshwater crab records from northern Vietnam 1996 1984); and C. xingrenense Dai & Naiyanetr, 1994 (cf. Dai et al. 1980; Song 1984; Dai and Naiyanetr 1994; Dai 1999; Ng 2017; Zou et al. 2018). Le et al. (2024) first recorded the genus from Cao Bang and Quang Ninh provinces in northern Vietnam; describing one new species (Chinapotamon insulare Le, Dang & Do, 2024) and provisionally extending the distributions of two taxa (C. cf. depressum and C. cf. pusillum). Re-examination of the Chinapotamon specimens provisionally identified as C.depressum and C.pusillum showed that the “C. cf. depressum” from Cao Bang province is a new species (described herein), while “C. cf. pusillum” from Quang Ninh province is shown to be C. pusillum sensu stricto. In addition, the first author also collected several specimens of a small semi-terrestrial species of potamid freshwater crab from Ha Giang province, northern Vietnam, which after morphological examination, proved to be Songpotamon malipoense Shi, Pan & Sun, 2023. This genus, together with two other species (S. dixuense Naruse, Chia & Zhou, 2018, S. funingense Shi, Pan & Sun, 2023 [type species]) had previously only been recorded from Yunnan province, in China (see Shi et al. 2023). Here we describe the new species of Chinapotamon (C. halangense sp. nov.) and report two new country records (C. pusillum and Songpotamon malipoense). With these three additions, this work raises the total number of potamid species found in Vietnam to 65. Materials and methods Specimens of Chinapotamon and Songpotamon were hand collected from northern Vietnam,and subsequently preserved in 70–95% ethanol. The specimens were examined under a Nikon SMZ18 and Leica M80 stereomicroscope and photos of the male first and second gonopods were taken using a Leica M125C stereomicroscope. Photographs were taken using Nikon D5600 digital single-lens reflex or Nikon Z8 mirrorless camera. The drawings were done using camera lucida attachment mounted on the stereomicroscope before being processed with Adobe Photoshop CS5 and Adobe Illustrator CS2 graphics software. Materials examined are deposited at the Institute of Biology (IB), Vietnam Academy of Science and Technology (VAST); the Zoological Reference Collection (ZRC) of the Lee Kong Chian Natural History Museum, National University of Singapore; and the Chinese Academy of Sciences (CAS), Beijing, China. The following abbreviations are used: CL = maximum carapace length; CW = maximum carapace width; G1 and G2 = male first and second gonopods, respectively. Measurements, in millimeters (mm), are of the carapace width (CW) by carapace length (CL), as well as the ratio of length/width of the second and fourth ambulatory leg segments. The terminology used here essentially follows that used by Ng (1988, 2017), Davie et al. (2015). Systematics Family Potamidae Ortmann, 1896 Genus Chinapotamon Dai & Naiyanetr, 1994 Chinapotamon halangense sp. nov. https://zoobank.org/FD1B3A36-C9E6-450E-B546-83C212C0BEE6 Figs 1–3 Chinapotamon cf. depressum – Le et al. 2024: 504–507, figs 2, 3, 10A. (not Tiwaripotamon depressum Dai, Song, Li & Liang, 1980) Material examined. Holotype • 1 male (34.9 × 26.8 mm) (IB-FC-CHx01), 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. Paratypes • 2 males (34.4 × 26.3 mm, 32.5 × 25.2 mm), 1 female (27.2 × 21.3 mm) (ZRC 2024.0312), same data as holotype • 1 male (31.5 × 24.8 mm), 1 female (33.9 × 26.6 mm) (IB-FC-CHx03), 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. • 1 male (31.1 × 24.9 mm), 1 female (27.8 × 21.8 mm) (IB-FC-CHx04) 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. • 1 male (27.9 × 21.5 mm), 1 female (33.8 × 26.2 mm) (IB-FC-CHx05), 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. Diagnosis. Carapace (Fig. 1A) 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. 1D). Male major chela oblate wide gape when closed (Fig. 1E). Ambulatory legs relatively slender; length to width ratio of last ambulatory merus = 2.5 (Fig. 1A). Thoracic sternites 3 and 4 without trace of groove demarcating suture (Fig. 2A). Male telson relatively broad, lateral margins slightly convex (Fig. 2A). 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). 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. 1A). Zoosyst. Evol. 101 (4) 2025, 1995–2012 zse.pensoft.net 1997 Figure 1. Chinapotamon halangense sp. nov. Holotype, male (34.9 × 26.8 mm) (IB-FC-HLx01). A. Overall dorsal habitus; B. Frontal view of cephalothorax; C. Antennae, antennule and epistome; D. Left third maxilliped; E. Chelipeds (lateral view). zse.pensoft.net Do, V.T. et al.: A new species of Chinapotamon and two new freshwater crab records from northern Vietnam 1998 Figure 2. Chinapotamon halangense sp. nov. A, B. Holotype male (34.9 × 26.8 mm) (IB-FC-HLx01); C. Paratype female (33.9 × 26.6 mm) (IB-FC-HLx03); D. paratype female (33.8 × 26.2 mm) (IB-FC-HLx05). A, C. Ventral view, with pleon closed; B. Sternopleonal cavity with G1s and G2s in situ; D. Sternopleonal cavity and vulvae. 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. 1A, B). Epigastric cristae distinct, not sharp, separated by broad, shallow Y-shaped furrow, separated from postorbital cristae by short, shallow groove; postorbital cristae low (Fig. 1A). Cervical grooves shallow but distinct; H-shaped median gastric groove shallow but distinct (Fig. 1A). Frontal margin divided into 2broad, low lobes, separated by broad, very shallow concavity; margin of each lobe gently convex, confluent with supraorbital margin (Fig. 1A). 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. 1A). Anterolateral margins distinctly cristate, lined with granules (Fig. 1A). Posterolateral margin strongly converging towards posterior carapace margin (Fig. 1A). Orbits subovate; eye filling orbit; ocular peduncle long; cornea normal (Fig. 1B). Supraorbital margin weakly concave, entire, lined with small, flattened granules (Fig. 1B). Suborbital margin concave, complete, lined with small granules (Fig. 1B). Posterior margin of epistome with distinct broad median triangle, each lateral margin with 2 lateral concavities (Fig. 1C). 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. 1D). Male chelipeds asymmetrical in size (Fig. 1A, E). Anterior margin of basis-ischium almost smooth; inner-lower margins of merus granulated (Fig. 1E). Outer surface of carpus gently rugose, inner distal angle with distinct sharp tooth, with 2 smaller teeth basally (Fig. 1A). Outer surfaces of chelae with numerous pits, otherwise smooth; Zoosyst. Evol. 101 (4) 2025, 1995–2012 zse.pensoft.net 1999 chela palm in large males approximately 1.3 times as long as broad; major chela stouter, longer than minor chela (Fig. 1E). 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. 1E). Fingers of minor chela slender, shorter than major chela, fingers relative straight, with small gape when closed (Fig. 1E). Ambulatory legs not elongated, slender; second pair longest, last pair shortest (Fig. 1A). 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. 1A). Thoracic sternites relatively broad transversely (Fig. 2A). 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. 2B). Male pleonal locking tubercle just aft of median part of sternite 5 (Fig. 2B). 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. 2A). Figure 3. Chinapotamon halangense sp. nov., A, B, F, G. Left G1s; E. G2; C, D, H, J. G1 terminal articles. A–E. Holotype, male (34.9 × 26.8 mm) (IB-FC-HLx01); F, H. Paratype, male (34.4 × 26.3 mm) (ZRC 2024.0312); G, J. Male, (32.5 × 25.2 mm) (ZRC 2024.0312). A, C, F, G, H, J. Ventral view; B, D. Dorsal view. Scale bars: 1 mm. zse.pensoft.net Do, V.T. et al.: A new species of Chinapotamon and two new freshwater crab records from northern Vietnam 2000 G1 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 G2 visible in ventral orientation (Fig. 3). G2 longer than G1, 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. 2C). 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. 2D). 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. 10A). 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). 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 G1 subterminal article and the G1 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 G1 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. 1A) (vs. carapace subquadrate and comparatively rugose, particularly around branchial regions, cf. Fig. 5A); (2) epigastric and postorbital cristae faint (Fig. 1A) (vs. well-developed epigastric and postorbital cristae, cf. Fig. 5); (3) external orbital tooth positioned lower than frontal margin (Fig. 1A) (vs. external orbital tooth positioned higher than frontal margin, cf. Fig. 5); (4) suture separating sternites 3 and 4 barely visible (Fig. 1A) (vs. suture separating sternites 3 and 4 prominent, cf. Fig. 5); Figure 4. Habitat of Chinapotamon halangense sp. nov. A. Karst hill in Duc Quang Commune, Ha Lang District, Cao Bang Province; B. Shallow seepage and streams where C. halangense sp. nov. was collected from. Zoosyst. Evol. 101 (4) 2025, 1995–2012 zse.pensoft.net 2001 Figure 5. Chinapotamon depressum (Dai, Song, Li & Liang, 1980). Holotype male (CAS CB-05199). A. Overall dorsal habitus; B. Frontal view of cephalothorax; C. Ventral view; D. Left G1 (ventral view); E. Left G1 (dorsal view). zse.pensoft.net Do, V.T. et al.: A new species of Chinapotamon and two new freshwater crab records from northern Vietnam 2002 (5) ambulatory legs slenderer, merus and propodus of last ambulatory leg 3.5 and 2.3 times as long as wide respectively (Fig. 1A) (vs. ambulatory legs stouter, merus and propodus of last ambulatory 3.3 and 2.1 times as long as wide, respectively, cf. Fig. 5; Dai 1999; Ng 2017: table 1; Zou et al. 2018: table 2); (6) major chela fingers forming large ovate gape when closed (Fig. 1E) (vs. major chela fingers forming no gape when closed, cf. Fig. 5; Dai 1999: pl. 4, fig. 5; cf. Zou et al. 2018: table 2); (7) telson broadly triangular, lateral margins slightly convex (Fig. 2A) (vs. telson acutely triangular, lateral margins straight, cf. Fig. 5); and (8) G1 subterminal article basal part proportionally longer, with shorter, broader neck-like distal half (Fig. 3) (vs. G1 subterminal article basal part proportionally shorter, to proximal third of article, with longer, more slender distal neck-like part, cf. Fig. 5D, E). Chinapotamon pusillum (Song, 1984) Figs 6–8, 10 Tiwaripotamon pusillum Song, 1984: 143–145, figs 1–9 Chinapotamon pusillum Dai & Naiyanetr, 1995: 63, fig. 10; Dai, 1999: 91–92, fig. 42; Ng et al. 2008: 161; Cumberlidge et al. 2009: table A1. Chinapotamon cf. pusillum Le et al. 2024: 507–509, figs 4, 5, 10B. Material examined. Holotype • 1 male (CAS CB-05188). Others • 1 male (15.9 × 14.2 mm) (IB-FC-CMx01), a small stream flowing into the rice canal, in Song Mooc village, Dong Van Commune, Binh Lieu District, Quang Ninh Province, 21°33'11.5"N, 107°34'21.2"E, 22 March 2023, Do Van Tu leg. • 6 males (14.2 × 12.3 mm, 12.3 × 10.9 mm,12.2 × 11.4 mm, 11.7 × 10.4 mm, 11.2 × 10.1 mm, 11.0 × 9.8 mm), 6 female (21.0 ×18.0 mm, 20.0 × 16.5 mm,17.8 × 15.1 mm, 17.3 × 14.0 mm, 13.7 × 11.7 mm, 12.4 ×10.8 mm) (IB-FC-CMx02), same data as above • 2 males (17.0 × 14.3 mm, 14.8 × 13.9 mm), 1 female (21.2 × 17.3 mm) (ZRC2024.0313), same data as above. Diagnosis. Diminutive species (adult carapace width range between 14.0–21.0 mm). Carapace slightly wider than long, subquadrate, rugose, gently convex, region not distinct, indistinctly separated (Fig. 6A). Epigastric and postfrontal cristae distinct (Fig. 6A). External orbital and epibranchial teeth low; cleft between external orbital and epibranchial teeth deep (Fig. 6A). Anterolateral margin of carapace slightly convex, cristate (Fig. 6A). Exopod of third maxilliped reaching to 0.2 times length of merus with flagellum longer than width of merus (Fig. 6). Male major chela no gape when closed (Fig. 6E). Ambulatory legs not elongated (Fig. 6A). Sternites 3 and 4 without trace of groove demarcating suture (Fig. 7A). Male telson relatively broad, lateral margins almost straight (Fig. 7A). G1 slender, sinuous, terminal article bent about 25° outward proximally, recurved distally, tip directed vertically (Fig. 8). Description of Vietnamese specimens. Carapace subquadrate, slightly wider than long, CW:CL ratio = 1.1 (median = 1.1); dorsal surface rugose, finely pitted, gently convex transversely, gently convex antero-posteriorly, regions poorly defined (Fig. 6A). Frontal region rugose; lateral parts of anterolateral, hepatic and branchial regions rugose; protogastric, mesogastric, urogastric, cardiac and intestinal regions almost smooth except for pits; orbital regions slightly rugose; suborbital and pterygostomial regions rugose (Fig. 6A, B). Epigastric cristae low, distinct, not sharp, separated by broad, shallow Y-shaped furrow, confluent with postorbital cristae; postorbital cristae low (Fig. 6A). Cervical grooves shallow, indistinct; H-shaped median gastric groove shallow but distinct (Fig. 6A). Frontal margin divided into two broad, low lobes, separated by broad, shallow concavity; margin of each lobe gently convex, confluent with supraorbital margin (Fig. 6A). External orbital tooth low, demarcated from rest of anterolateral margin by small, shallow notch; epibranchial tooth low (Fig. 6A). Anterolateral margins distinctly cristate, lined with small granules (Fig. 6A). Posterolateral margin gently converging towards posterior carapace margin (Fig. 6A). Orbits subovate; eye filling orbit; ocular peduncle long; cornea normal (Fig. 6B). Supraorbital margin weakly concave, entire, lined with small, flattened granules (Fig. 6 B). Suborbital margin concave, complete, lined with small granules (Fig. 6B). Posterior margin of epistome with distinct broad median triangle, each lateral margin with 2 lateral concavities (Fig. 6C). Ischium of third maxilliped subrectangular, about 1.5 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; exopodslender, reaching to 0.2 times length of merus, flagellum distinct, longer than width of merus (Fig. 6D). Chelipeds slightly asymmetrical, relatively stout, no significant difference in asymmetry between males and females (Fig. 6E). Anterior margin of basis-ischium almost smooth; inner-lower margins of merus granulated (Fig. 6E). Outer surface of carpus gently rugose, inner distal angle with distinct sharp tooth, with 2 smaller teeth basally (Fig. 6A). Outer surfaces of chelae smooth; chela palm in large males approximately 1.3 times as long as broad; major chela stouter, longer than minor chela (Fig. 6E). 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, very small gape when closed, tips slightly cross (Fig. 6E). Fingers of minor chela slender, fingers relative straight, almost no gap when closed (Fig. 6E). Ambulatory legs not elongated; second pair longest, last pair shortest (Fig. 6A). Outer surface of merus slightly rugose, dorsal margin weakly serrated, length to width ratio of fourth merus = 3.0; carpus slightly rugose, outer surface with submedian crista on first to third legs; propodus subrectangular; length to width ratio of fourth propodus = 1.5; dactylus gently curved, margins with short, sharp pectinate spines on both inner and outer margins (Fig. 6A). Thoracic sternites relatively broad transversely (Fig. 7A). Sternites 1, 2 completely fused to form broadly triangular plate; separated from sternite 3 by complete suture; Zoosyst. Evol. 101 (4) 2025, 1995–2012 zse.pensoft.net 2003 Figure 6. Chinapotamon pusillum (Song, 1984), Vietnam. Male (17.0 × 14.3 mm) (ZRC2024.0313). A. Overall dorsal habitus; B. Frontal view of cephalothorax; C. Antennae, antennule and epistome; D. Left third maxilliped; E. Chelipeds (lateral view). zse.pensoft.net Do, V.T. et al.: A new species of Chinapotamon and two new freshwater crab records from northern Vietnam 2010 Figure 13. Songpotamon malipoense Shi, Pan & Sun, 2023, Vietnam. A, B. Male, (18.9 × 14.7 mm) (IB-FC-SMx01); C, D. Female, (15.3 × 12.4 mm) (IB-FC-SMx01). A, C. Ventral view, with pleon closed; B. Sternopleonal cavity with right G1 in situ; D. Sternopleonal cavity and vulvae. Figure 14. Songpotamon malipoense Shi, Pan & Sun, 2023, Vietnam. Male, (21.8 × 16.3 mm) (ZRC 2024.0321), Left G1, A. Ventral view; B. Oblique ventral view; C. Dorsal view. Scale bar: 1 mm. Zoosyst. Evol. 101 (4) 2025, 1995–2012 zse.pensoft.net 2011 The three species of freshwater crabs discussed in this study are restricted to mountainous areas along the border between Vietnam and China and are highly vulnerable to habitat degradation. One species was found within a protected forest, but most of the surrounding habitat has been converted into agricultural land with rice, maize and cassava as the dominant crops. Additional threats include the use of agrochemicals (e.g., herbicides and pesticides), soil erosion leading to stream sedimentation, and occasional harvesting by local communities. To safeguard the long-term survival of these species, conservation efforts should focus on protecting and restoring the remaining forest patches, maintaining clean and stable freshwater sources, and promoting environmentally friendly agricultural and forestry practices. Acknowledgements This research was funded by the Vietnam Academy of Science and Technology under grant number CSCL09.02/2425. Bui Thuy Linh is thanked for measuring the specimens in IB. We would also like to express our appreciation to Arthur E. Bogan for his kind help in improving an earlier version of the manuscript. We are grateful to Zhou Xian Min, Tohru Naruse and the late Ng Ngan Kee for the photographs of the types of C. depressum and C. pusillum. 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