Indochinamon datii, Dang & Hoang & Do, 2024

Dang, Khai, Hoang, Anh Tram & Do, Cuong, 2024, A new species of the genus Indochinamon Yeo & Ng, 2007 (Crustacea: Brachyura: Potamoidea: Potamidae) and a new country record from Northern Vietnam, Zootaxa 5437 (4), pp. 560-570 : 561-567

Indochinamon datii n. sp.

( Figs. 1–6 )

Material examined. Holotype: male (61 × 49 mm), ( VNMN 2022.001 ), mainstream, Ban Coi, Xuan Son National Park, Tan Son district , Phu Tho Province (21.140°N, 104.942°E), coll. local people, 18 June 2022 . Paratypes: 2 males (60 × 46 mm, 66 × 51 mm), 1 female (60 × 47mm) (Experta collection 2023.001; 2023.002; 2023.003), main stream, Ban Coi, Xuan Son National Park , Tan Son district , Phu Tho Province (21.140°N, 104.942°E), coll. Khai Dang, 18 March 2023 ; 1 male (51 × 35 mm), 1 female (43 × 31 mm) ( ZRC 2024.0014 ), main stream, Ban Coi, Xuan Son National Park, Tan Son district , Phu Tho Province (21.140°N, 104.942°E), coll. Cuong Do, 18 March 2023 .

Diagnosis. Carapace transversely ovate, broader than long, dorsal surface glabrous, nearly flat; regions indistinctly defined, frontal and orbital regions rugose, lateral parts of anterolateral and branchial regions granulose, anterolateral margin lined with granules ( Fig. 1A ). Cervical grooves shallow, not reaching lateral margins, connected to deep H-shaped median gastric groove ( Fig. 1A ). Frontal margin appearing entire in dorsal view, almost straight in frontal view ( Fig. 1A, B ). Third maxilliped exopod with elongate and slender flagellum that reaches two-third of merus width ( Fig. 2A ). Outer surfaces of chela lined with prominent granules ( Fig. 1D, E ). Fingers of major chela short, stout, slightly curved inwards, subequal in length to palm, outer surface lined with nodules; cutting edges of both fingers with variously sized sharp teeth and denticles. Minor chela similar to major chela in form but relatively more slender ( Fig. 1A, D, E ). Male pleon triangular, lateral margin of sixth somite slightly convex, gradually decreasing in width, increasing in length. Telson broadly triangular, lateral margin slightly concave, almost straight, tip rounded ( Fig. 1C ). G1 relatively stout, terminal segment slightly curved, subterminal segment about 3.3 times as long as terminal segment, G1 curving outwards. G2 elongate, strongly curved, much longer than G1.

Description of holotype male: Carapace transversely ovate, markedly wider than long (width-to-length ratio 1.2); dorsal surface flat from the frontal view, glabrous, regions not prominent ( Fig. 1A ). Frontal and orbital regions rugose; lateral parts of anterolateral and branchial regions granulose; mesogastric, urogastric, cardiac and intestinal regions smooth; suborbital region smooth; pterygostomial, subhepatic and subbranchial regions smooth to weakly granulose ( Fig. 1B ). Epigastric cristae distinct, not sharp, weakly granulose, separated by narrow, median Y-shaped furrow; postorbital cristae distinct, margin uneven, slightly raised, subparallel to frontal margin, lateral edge relatively low and not prominent ( Fig. 1A ). Cervical grooves shallow, not reaching lateral margins, connected to deep H-shaped median gastric groove ( Fig. 1A ). Frontal margin almost straight, appears entire in dorsal view ( Fig. 1A, B ). External orbital tooth distinct, broadly triangular, demarcated from rest of anterolateral margin by deep V-shaped cleft; epibranchial tooth prominent, sharp ( Fig. 1A, B ). Anterolateral margins convex, lined with sharp granules, weakly serrated ( Fig. 1A, B ). Posterolateral margin converging posteriorly ( Fig. 1A ). Orbits subovate; eye filling orbital space, eye peduncle relatively short, stout; cornea large, round ( Fig. 1B ). Supraorbital margin relatively straight ( Fig. 1A ). Suborbital margin concave, complete, lined with low granules ( Fig. 1B ). Antennae short, stretching across base of eyes; antennules short, folding transversely in subrectangular fossae ( Fig. 1B ). Posterior margin of epistome sinuous with distinct median triangle, lateral margin sinuous ( Fig. 1B ).

Third maxillipeds covering most of buccal cavity when closed; ischium subrectangular with distinct median groove, surface glabrous with scattered shallow pits; merus subquadrate, slightly wider than long, surface smooth, margins cristate; exopod slender, reaching to about one-third length of merus, with elongate and slender flagellum that reaches two-thirds of the merus width ( Fig. 2A ).

Thoracic sternum relatively broad, surface with scattered shallow pits and short notches ( Fig. 1C ). Sternites 1, 2 merged completely to form broadly triangular plate; separated from sternite 3 by distinct, gently concave suture; sternites 3, 4 completely fused, with shallow incomplete groove demarcating suture ( Fig. 1A , 2B ). Sternopleonal cavity reaching to imaginary line joining median part of cheliped coxae. Male pleonal locking tubercle low, round, between the anterior and posterior margins of sternite 5 ( Fig. 2B ).

Chelipeds asymmetrical, right cheliped slightly larger ( Fig. 1A ). Anterior margin of basis-ischium smooth; margins of merus lined with low sharp granules, appearing serrated. Outer surface of carpus rugose with granules, inner distal angle with large sharp tooth and basal tooth ( Fig. 1D ). Outer surfaces of chelae strongly granulose, upper part rugose with granules, major chela stouter and shorter than minor chela ( Fig. 1A ). Fingers of major chela short, stout, slightly curved inwards, subequal to palm, outer surface lined with nodules; cutting edges of both fingers with variously sized sharp teeth and denticles; dorsal margin of dactylus with prominent tubercles ( Fig. 1A, D, E ). Fingers of minor chela similar to major chela in form but relatively more slender ( Fig. 1A, E ).

Ambulatory legs short, segments relatively stout; second pair longest (about 1.5 times longer than carapace width), last pair shortest (about 1.4 times longer than carapace width) ( Fig. 1A ). Merus short, stout (length to width ratio: 3.5), outer surface rugose, dorsal margin uneven, subcristate, without subdistal spine or tooth; carpus rugose, dorsal margin with cristate, outer surface with low submedian cristate on first to third legs but absent on fourth legs; dorsal margin of propodus with cristate, outer surface with low, submedian cristate; dactylus relatively short, slender, nearly straight, margins with short, sharp pectinate spines ( Fig. 1A ).

Pleon narrowly triangular, all somites and telson free; telson broadly triangular, lateral margins nearly straight; somite 6 transversely rectangular, wider than long, lateral margin straight; somites 2–5 trapezoidal, gradually decreasing in width, increasing in length; somite 1 subrectangular, very wide, reaching to bases of coxae of fourth ambulatory legs, thoracic sternite 8 not visible when pleon closed ( Fig. 1C ).

G1 relatively stout; subterminal segment gently sinuous, about 3.3 times as long as terminal segment. Terminal segment broad, subconical, gently curved, gradually tapering to median part, slightly separated from subterminal segment, slightly inflated proximally, distal part tapered, gently curving outwards, tip pointed. Subterminal segment with thin cleft on distal part ( Fig. 2B, D, E ). G2 elongate, strongly curved, much longer than G1, basal segment longer than distal segment about 1.4 times, G2 base is nearly round, wide in the middle and slightly narrow to the top ( Fig. 2H ).

Description of paratype female: Female with similar external morphological features to males. Pleon subovate, wide, covers entire thoracic sternum when closed ( Fig. 3A ). Female vulvae on thoracic sternite 5/6, subquadrate, opening directed mesially, opening covered with membrane ( Fig. 3B ).

Etymology: The species is named after Mr. Dat Pham (Hanoi, Vietnam), who is an active member of this research team involved in both field trips and laboratory work.

Live colouration: The crabs usually display two main colour morphs: brownish-green with light orange margin and yellowish-orange ( Fig. 4 ), several intermediate colour form are reported. There is no distinct difference in morphology between individuals of different colours. Similar colour variation also can be seen in other species of Indochinamon ( Zhang et al. 2020) .

Habitat: The stream in Xuan Son National Park from where the specimens were collected is a fast-flowing stream in the rainy season. The substrate consists of rocks of different sizes with a sandy bank, mixed with pebbles of various sizes, and driftwood. Trees, ferns, and vines that grow along the banks of the stream. Another smaller branch of the stream has slow-flowing water, many aquatic and semi-aquatic plants grow on rocks or in the stream bed including Bolbitis ferns, watercress, and aroids ( Fig. 5B ). In the dry season, the water in both branches dries up, revealing the rocky bottom with large fallen tree trunks. Only a few pools remain, fed by small and slow-flowing streamlets ( Fig. 5A ). This species also occurs in other streams in the National Park. Other syntopic species found in the stream include gobies ( Rhinogobius sp. ), loaches ( Schistura spp. ), snakeheads ( Channa sp. ), dwarf shrimps ( Caridina spp. ), freshwater prawns ( Macrobrachium spp. ), Indochinamon mieni (Dang, 1967) , pachychilid snails, aquatic and semi-aquatic insects of Coleoptera, Hemiptera, Odonata, Ephemeroptera and Plecoptera. The population of this crab is large and stable due to its wide distribution in a well-protected area and clean water quality was observed during 2 years of fieldwork and surveys conducted by the locals in the national park despite being frequently captured for food and sold to tourists by locals. Locals capture the crabs using a long stick baited with worms to lure the crabs out of the rock crevices.Adults often hide in rock crevices in stream beds and are sometimes found scuttling on the forest floor at night. Young individuals usually live in areas with slow-moving water. This species usually feeds at night and is rarely seen during the day.

Remarks. The new species is most similar to I. kimboiense (Dang, 1967) and I. bavi Naruse, Nguyen & Yeo, 2011 , due to the shape of the carapace and strong granulation on the dorsal surface of carapace and chelipeds ( Fig. 1A, D, E ; cf. Naruse et al. 2011: figs. 1A, 2B, 4A, 5B). Indochinamon datii n. sp. can be distinguished from these two species by the following: 1) I. datii n. sp. has more grannulose carapace on the dorsal and frontal surface ( Fig. 1A ) than I. bavi (cf. Naruse et al. 2011: fig. 4A) but less prominent than I. kimboiense (cf. Naruse et al. 2011: fig. 1A); 2) the dorsal carapace regions are less defined in I. datii n. sp. ( Fig. 1A ) than in the two other species ( Naruse et al. 2011: figs. 1A, 4A); 3) the dorsal surface of the new species is relatively flatter ( Fig. 1B ) than I. kimboiense (cf. Naruse et al. 2011: fig. 2A), while that of I. bavi is slightly convex longitudinally (cf. Naruse et al. 2011: fig. 5A); 4) the frontal margin is nearly straight ( Fig. 1B ), while that of I. bavi is gently convex (cf. Naruse et al. 2011: fig. 5A) and that of I. kimboiense is gently sinuous (cf. Naruse et al. 2011: fig. 2A); 5) the male telson is broadly triangular with the lateral margins nearly straight ( Figs. 1C , 2C ) while it is broadly triangular, with lateral margins slightly concave in I. kimboiense (cf. Naruse et al. 2011: fig. 1B), the telson of I. datii n. sp. is relatively shorter than that of I. bavi ( Figs. 1C , 2C ), (cf. Naruse et al. 2011: fig. 4B). The G1 characteristics of all three species are similar, however the G1 of I. datii n. sp. is more slender and curved ( Fig. 2D, E ) than those of the other two species, and the soft joint between the two segments of the new species is also more constricted ( Fig. 2D, E ) while that in the other two species narrowed steadily to the terminal segment (cf. Naruse et al. 2011: fig. 3A, B, D, E). Furthermore, the G1 terminal segment is slightly curved in I. datii n. sp. ( Fig. 2D, E ) (versus nearly straight in the two other species; cf. Naruse et al. 2011: fig. 3A, B, D, E).

Indochinamon datii n. sp. also resembles I. ahkense Naruse, Chia & Zhou, 2018 , by having G1 with relatively slender terminal segment and pointed tip. However, I. datii n. sp. can be distinguished from I. ahkense by the following: 1) the regions on carapace not appearing prominently demarcated, with glabrous surface ( Fig. 1A ) (versus regions less demarcated, with short, indistinct setae on metabranchial region; cf. Naruse et al. 2018: fig. 2A); 2) the carapace of I. datii n. sp. is transversely ovate and the postorbital cristae are distinct, with uneven margin, and is slightly raised ( Fig. 1A, B ) while the carapace of I. ahkense is subquadrate, postorbital cristae rounded, not reaching epibranchial tooth and less granulose (cf. Naruse et al. 2018: fig. 2A); 3) the posterior margin of the epistome is sinuous with distinct median triangle in I. datii n. sp. ( Fig 1B ) (versus nearly straight, forming an arc shape in I. ahkense ; cf. Naruse et al. 2018: fig. 2B); 4) the G1 terminal segment of I. datii n. sp. is slender, curved and tapered to the tip ( Fig 2D, E ) while that of I. ahkese is broad and almost straight with stouter tip (cf. Naruse et al. 2018: fig. 4A, B, C).

Figures

FIGURE 1. Indochinamon datii n. sp. holotype, male (61 × 49 mm) (VNMN 2022.001); A, dorsal habitus; B, frontal view of cephalothorax; C, anterior thoracic sternum and pleon, ventral view; D, outer view of major chela; E, outer view of minor chela (dactylus tip broken).

FIGURE 2. Indochinamon datii n. sp. holotype, male (61 × 49 mm) (VNMN 2022.001);A, left third maxilliped, external view; B, sterno-pleonal cavity with G1 and G2 in situ, ventral view; C, male pleon, external view; D, left G1, ventral view; E, left G1, dorsal view; F, distal part of left G1, ventral view; G, distal part of left G1, dorsal view; H, left G2, dorsal view.

FIGURE 3. Indochinamon datii n. sp. paratype, female (60 × 47 mm) (Experta collection 2023.003); A, pleon, ventral view; B, thoracic sternum and vulvae, ventral view.

FIGURE 4. Indochinamon datii n. sp., colour in life. A, brownish-green form, dorsal view, male, from type locality, specimen not collected; B, brownish-green form, frontal view, male, from type locality, specimen not collected; C, yellowish-orange form, dorsal view, male, from type locality, specimen not collected; D, yellowish-orange form, frontal view, male, from type locality, specimen not collected.

FIGURE 5. Habitat of Indochinamon datii n. sp. in Xuan Son National Park. A, during the dry season on 18 March 2023; B, during the rainy season on 9 July 2022.

FIGURE 6. Indochinamon datii n. sp., holotype, male (61 × 49 mm) (VNMN 2022.001). A, left third maxilliped, external view; B, left G1, ventral view; C, left G1, dorsal view; D, left G2, dorsal view; E, distal part of left G1, ventral view; F, distal part of left G1, dorsal view.