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.

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).

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).

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). 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; 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 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.

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.

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.

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).

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).

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

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.

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).

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.

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); (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).

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).

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.

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).

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).

Figure 7. 

Chinapotamon pusillum (Song, 1984), Vietnam. A, B. Male (17.0 × 14.3 mm) (ZRC2024.0313); C, D. Paratype female (21.0 × 18 mm) (IB-FC-CMx02). A, C. Ventral view, withpleon closed; B. Sternopleonal cavity with right G1 in situ; D. Sternopleonal cavity and vulvae.

Figure 8. 

Chinapotamon pusillum (Song, 1984), Vietnam, G1s and G2. A–E. Male (17.0 × 14.3 mm) (ZRC2024.0313), F–H. Male (15.9 × 14.2 mm) (IB-FC-CMx01). A, B, F, G. G1s; C, D, H. G1 terminal articles; E. G2. A, C, G, H. Ventral view; B, D, F. Dorsal view. Scale bars: 1 mm.

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; sternites 3, 4 completely fused, without suture; sternopleonal cavity reaching to imaginary line connecting bases of cheliped coxae (Fig. 7B). Male pleonal locking tubercle at median part of sternite 5. Male pleon triangular; telson relatively broad with lateral margins almost straight, width to length ratio = 1.3; somite 6 broadly rectangular, width to length ratio = 2.4 (Fig. 7A).

G1 slender, reaching to suture between sternites 4 and 5 with terminal and subterminal articles clearly demarcated; subterminal articles relatively slender, sinuous, proximal half sub-trapezoidal, wider than distal half, tapering gently distally, directed inward proximally but outward distally, 2.1 times as long as terminal article; terminal article slender, relatively gradually tapering, bent about 25° outward, tip not pointed, with groove for G2 visible in ventral orientation (Fig. 8). G2 slightly longer than G1, distal article long, ratio of basal article to distal article = 2.1.

Females. Female specimens similar to male in most non-sexual features. Female pleon ovate in mature individuals, covering thoracic sternites (Fig. 7C). Vulvae set relatively far apart, small, subovate; directed ventral-mesially, positioned on proximal half of sternite 6 (Fig. 7D).

Dorsal surfaces brown; ventral surface white; outer and inner surfaces of chelae light yellow (cf. Le et al. 2024: fig. 10B).

This species is currently known from Dong Van Commune, Binh Lieu District, Quang Ninh Province, Vietnam and Fangcheng District, Guangxi Province, China.

This species inhabits small streams and crevices with stagnant or slow-flowing water, where the banks are densely vegetated with shrubs and the substrate is rich in organic detritus (Fig. 9). Juveniles of Indochinamon spp. were also observed in the same habitat.

Figure 9. 

Habitat of Chinapotamon pusillum (Song, 1984) in Vietnam, small stream flowing into the rice canal, Ban Song Mooc village, Dong Van Commune, Binh Lieu District, Quang Ninh Province.

Figure 10. 

Chinapotamon pusillum (Song, 1984), holotype, male (CAS CB-05188). A. Overall dorsal habitus; B. Frontal view of cephalothorax; C. Ventral view; D. Left G1 (ventral view); E. Left G1 (dorsal view).

The discovery of Chinapotamon pusillum (Song, 1984), in northern Vietnam may not come as a surprise, especially considering the similar geography of the area, with China. The Vietnamese specimens were collected from Dong Van Commune, Binh Lieu District, Quang Ninh Province, Vietnam, an area directly bordering Fangcheng District, Guangxi Province, southern China, which is the type locality of C. pusillum (Fig. 15). The two areas are part of a contiguous mountain range known as Shiwan Mountain (Hu et al. 2023); it is very possible that the species is distributed throughout the range.

Differences between C. pusillum (Song, 1984) and its closest congener, C. insulare, have been discussed in detail in Le et al. (2024). However, Le et al. (2024) treated specimens from Vietnam as C. cf. pusillum because they noted that they differed from the type description and figures in possessing more distinct anterolateral crista and a longer G1 terminal article that reaches to beyond the suture between thoracic sternites 4 and 5. We obtained fresh photographs of the holotype of C. pusillum (Fig. 10) and we can now confirm that there are no obvious differences in the strength of the anterolateral cristae (Fig. 6A). The difference noted in how far the G1 terminal article reaches beyond the suture between thoracic sternites 4 and 5 (Fig. 7B) can be affected by how much the male pleon is opened and flexed as well as the state of preservation of the specimens. Unfortunately, this is not apparent from the recent photographs of the holotype male. As such, we can only rely on the figure of this condition in Dai (1999: fig. 42.4) which may not have been drawn accurately. Nevertheless, on the basis of the available morphological characters and close geographical proximity, we are now confident they are actually conspecific with C. pusillum (Song, 1984) s. str. (Figs 6–8, 10, 15).

Morphologically, C. pusillum (Song, 1984) and C. insulare Le, Dang & Do, 2024, are quite distinct compared to congeners. These two species have a carapace that is more subquadrate and G1 terminal articles are directed more vertically, whereas in C. depressum (Dai, Song, Li & Liang, 1980), C. anglongense Dai & Naiyanetr, 1994, C. clarkei Ng, 2017, C. dashiwei Ng, 2017, C. glabrum (Dai, Song, Li & Liang, 1980), C. halangense sp. nov., C. longlinense Dai & Naiyanetr, 1994, C. maolanense Zou, Bai & Zhou, 2018 and C. xingrenense Dai & Naiyanetr, 1994, the carapace is more transversely subovate and the G1 terminal article is distinctively bent outwards (Figs 1, 5, 6, 10; cf. Ng 2017: figs 2, 6, 8; Zou et al. 2018: fig. 7, table 2). For now, C. pusillum and C. insulare will be retained in the genus Chinapotamon until the genus can be revised.

• 5 males (16.5 × 13.1, 17.0 × 13.8, 18.8 × 14.7, 18.9 × 14.7, 21.0 × 16.2 mm), 7 females (15.0 × 12.3, 15.3 × 12.4, 17.0 × 13.8, 17.8 × 14.3, 18.1 × 14.5, 18.9 × 14.7, 19.0 × 15.5 mm) (IB-FC-SMx01), a small stream in Khau Vai, Khau Vai Commune, Meo Vac County, Ha Giang Province, Vietnam, 23°4'55.3920"N, 105°29'34.4639"E, 22 Mar 2024, Do et al. leg. • 2 males (21.8 × 16.3 mm; 19.4 × 15.3 mm), 1 female (18.8 × 14.6 mm) (ZRC 2024.0321), same data as above.

None (see Shi et al. 2023 for full description).

This species has only been found in karst landscapes between Vietnam and China, namely, Malipo County, Wenshan Prefecture, Yunnan Province, southwest China, and Khau Vai Commune, Meo Vac District, Ha Giang Province, northern Vietnam.

This species was found in mud burrows on the banks of small hill streams (Fig. 11B). Field observations agree well with Shi et al.’s (2023) account of their material from Yunnan province, China; the present specimens collected from Ha Giang province, Vietnam, also exhibit a semi-terrestrial lifestyle.

Figure 11. 

Songpotamon malipoense Shi, Pan & Sun, 2023 in situ, Vietnam. A. Live colouration of Songpotamon malipoense from Vietnam; B. Mud burrows of S. malipoense; C, D. Habitat landscape of S. malipoense in Khau Vai Commune, Meo Vac District, Ha Giang Province, Vietnam.

The dorsal surface of the carapace is dark brown, brighter on the ventral surface, and orange on the chelae (Fig. 11A; cf. Shi et al. 2023: fig. 7A).

The examined specimens agree well with Songpotamon malipoense (see Shi et al. 2023). The specimens collected from Vietnam, like those from China are characterized by the following traits: relatively small adult carapace size (15.3–21 mm, n = 14); carapace broader than long, ovate; dorsal surface convex, smooth, pitted, regions not well defined; branchial regions swollen, smooth (Fig. 12A; cf. Shi et al. 2023: fig. 7A); postorbital and epigastric cristae inconspicuous, not confluent, separated by shallow groove; epigastric cristae weakly developed, oblique, separated by deep inverted Y-shaped groove; postorbital cristae low, weakly rugose (Fig. 12A; cf. Shi et al. 2023: fig. 7A); external orbital tooth bluntly triangular, outer margin convex, separated from anterolateral margin of carapace by shallow cleft (Fig. 12A; cf. Shi et al. 2023: fig. 7A); anterolateral margin of carapace convex, cristate, granular; posterolateral margin straight, with multiple weakly oblique striae (Fig. 12A; cf. Shi et al. 2023: fig. 7A); orbits large; suborbital regions smooth sub-hepatic and pterygostomial regions with small, rounded granules (Fig. 12B; cf. Shi et al. 2023: fig. 7B); median lobe of epistome posterior margin broadly triangular (Fig. 12C; cf. Shi et al. 2023: fig. 7B); exopod of third maxilliped without flagellum (Fig. 12D; cf. Shi et al. 2023: fig. 8C); chelipeds unequal in males (Fig. 12A; cf. Shi et al. 2023: fig. 7A); thoracic sternites 3, 4 in male fused except for relatively shallow, incomplete groove demarcating suture (Fig. 13A; cf. Shi et al. 2023: fig. 7C); male pleon narrowly triangular; somite 6 relatively narrow, width to length ratio 2.0 (Fig. 13A; cf. Shi et al. 2023: fig. 8E); G1 slender, reaching beyond pleonal locking tubercle up to suture between thoracic sternites 4 and 5 (Fig. 13B; cf. Shi et al. 2023: fig. 8G); subterminal article relatively slender, gently sinuous, inner margin almost straight; terminal article short, slender, subconical, relatively less strongly bent at about 30° angle outwards, about 0.4 times length of subterminal article, with distinct groove for G2 on ventral side, tip subtruncate, recurved upwards (Fig. 14; cf. Shi et al. 2023: fig. 9D, E); G2 longer than G1; terminal article relatively short; subterminal article about 3.0 times length of terminal article (Fig. 14; cf. Shi et al. 2023: fig. 9D); female pleon ovate, covering most of thoracic sternum (Fig. 13C; cf. Shi et al. 2023: fig. 8F); vulvae transversely ovate, closely located to each other, touching suture of thoracic sternites 5 and 6, opened inwards (Fig. 13D; cf. Shi et al. 2023: fig. 8H).

Figure 12. 

Songpotamon malipoense Shi, Pan & Sun, 2023, Vietnam. Male, (18.9 × 14.7 mm) (IB-FC-SMx01). A. Overall dorsal habitus; B. Frontal view of cephalothorax; C. Antennae, antennules and epistome; D. Right third maxilliped; E. Chelipeds (lateral view).

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.

Geographically, the Chinese and Vietnamese populations are separated by about 70 km (Fig. 15) of lowlands. The area where the Vietnamese specimens were collected is part of a larger karst landscape known as the Dong Van Karst Plateau, which itself is a contiguous extension of the South China karst belt (Yunnan karst plateau) (Tran et al. 2022) where the type locality of S. malipoense Shi, Pan & Sun, 2023, is located.

Figure 15. 

Map showing the distribution of Chinapotamon depressum, C. pusillum, C. insulare, C. halangense sp. nov., and Songpotamon malipoense in Vietnam and China.