Caridina tamkim, Do & Phan & von Rintelen & Le & von Rintelen, 2025

Do, Van Tu, Phan, Thi Yen, von Rintelen, Kristina, Le, Hung Anh & von Rintelen, Thomas, 2025, Descriptions of four new species of atyid shrimp (Crustacea, Decapoda, Atyidae) in Vietnam, ZooKeys 1247, pp. 151-186 : 151-186

Caridina tamkim sp. nov.

Figs 14 , 15 , 16 , 17

Type material.

Holotype. • Adult male, cl 4.8 mm, IB -FS 010 , Vietnam, Cao Bang Province, Nguyen Binh District, Tam Kim Commune , a small stream, 22°34'53.207"N, 106°1'46.368"E, 08 October 2020, collected by Van Tu Do . Paratypes. • 14 females, cl 3.8–5.8 mm, 5 males, cl 4.0– 5.4 mm, ZMB 32924 , same data as holotype ; • male, cl 4.5 mm, IB -FS 010 _ 2, Vietnam, same location as holotype, 21 March 2024, collected by Van Tu Do ; • two males, cl 4.4, 4.5 mm, female, cl 5.5 mm, 8 additional specimens, ZMB 32923 , Vietnam, Nguyen Binh District, Tam Kim Commune, Tran Hung Dao forest , a well at the inflow of small stream, 22°35'37.902"N, 106°2'35.897"E, 08 October 2020, collected by Van Tu Do, Dang Van Dong ; • 2 males, cl 4.3, 4.5 mm, 2 females, cl 5.0, 5.5 mm, 7 additional specimens, ZMB 33814 , Vietnam, Cao Bang Province, Nguyen Binh District , a small stream near the road, 22°38'16.626"N, 105°58'32.135"E, collected by Van Tu Do, Dang Van Dong, Nguyen Tong Cuong, 5 October 2020 ; • male, cl 4.7 mm, female, cl 4.4 mm, 4 additional specimens, ZMB 33793 , Vietnam, Cao Bang Province, Nguyen Binh District, Quang Thanh Commune, a small stream run out from Ong cave , 22°34'35.316"N, 105°55'25.998"E, collected by Van Tu Do, 7 October 2020 ; • male, cl 5.4 mm, female, cl 5.2 mm, 10 additional specimens, ZMB 33788 , Vietnam, Cao Bang Province, Nguyen Binh District , a small stream near the road, 22°38'20.82"N, 105°58'33.318"E, collected by Van Tu Do, 8 October 2020 .

Comparative material.

Caridina pacbo Do, von Rintelen & Dang, 2020 : • adult male, cl 4.2 mm, IB –FS 003 (Holotype), Vietnam, Cao Bang Province, Ha Quang District, Truong Ha Commune, Pac Bo Village , small stream in Khuoi Nam , 22°59'1.7"N, 106°02'31.2"E, 25 May 2017, collected by Van Tu Do.

Diagnosis.

This new species is characterized by several morphological characters such as short and slender rostrum, reaching just to the end of the basal segment of antennular peduncle or sometimes to the middle of second segment, without or with a few small teeth (Fig. 14 A ); medium stylocerite, reaching to the end of the basal segment or sometimes to beginning of second segment of the antennular peduncle (Fig. 14 B ); dactylus of the first pereiopod is shorter than palm (Fig. 15 A ); long, sub-rectangular endopod of the male first pleopod, extending to 0.87 of the length of the exopod, with short appendix interna, not or slightly exceeding the terminal margin of the endopod (Fig. 15 G, H ); short and stick-shaped appendix masculina of male second pleopod, reaching to proximal 0.8 of the length of the endopod, with narrow and small appendix interna, extending ~ 0.6 of the length of appendix masculina (Fig. 15 I, J ).

Description.

Cephalothorax and cephalic appendages. Carapace length 3.8–5.8 mm (median 4.6 mm, n = 20). Rostrum very short and slender, straight, mostly reaching near the end of basal segment of antennular peduncle, sometimes to middle of second segment, 0.1–0.2 (median 0.2) as long as carapace, teeth small, rostral formula 0–4 + 0 – 8 / 0 – 2 (Fig. 14 A ). Suborbital angle acute, completely fused with antennal spine; pterygostomian margin rounded, slightly produced forward (Fig. 14 A ). Eyes normally developed with globular cornea, eyestalk short, anterior end reaching to 0.6 of length of basal segment of antennular peduncle (Fig. 14 A ). Antennular peduncle 0.37–0.44 (median 0.43) × as long as carapace; basal segment 1.6–2.2 (median 1.67) × as long as second segment, second segment 1.2–1.25 (median 1.25) × as long as third segment (Fig. 14 B ). Stylocerite reaching to end of basal segment or sometime to beginning of second segment of antennular peduncle (Fig. 14 A, B ). Scaphocerite ovate, reaching beyond distal end of antennular peduncle, 2.33–2.67 (median 2.5) × as long as wide (Fig. 14 A, C ).

Abdominal somites, telson, and uropods. Sixth abdominal somite 0.3–0.42 (median 0.38) × length of carapace, 1.31–1.64 (median 1.42) × as long as fifth abdominal somite, 0.76–1.0 (median 0.89) × length of telson. Telson length 2.1–2.38 (median 2.25) × as long as proximal wide, distal margin triangular, terminating in a short median projection, with six pairs of dorsal spiniform setae and one pair of dorso-subdistal spiniform setae; distal end with three or four pairs of spiniform setae, lateral pair slightly shorter than intermediate pairs (Fig. 14 D, E ). Preanal carina moderately high, slightly bent backwards, with few setae, lacking a spine (Fig. 14 F ). Uropodal diaeresis with 17–20 (median 18) movable spiniform setae, outermost longer than lateral angle (Fig. 14 G ).

Mouthparts and branchiae. Incisor process of mandible ending in one row of six or seven irregular teeth, molar process truncated (Fig. 14 H ). Lower lacinia of maxillula broadly rounded, upper lacinia elongated, with several distinct teeth and setae on inner margin, palp stout with few simple setae at tip (Fig. 14 I ). Upper endites of maxilla subdivided, palp short, scaphognathite tapering posteriorly, with numerous long, curved setae at posterior margin (Fig. 14 J ). Distal end of palp of first maxilliped triangular, with a short projection; flagellum of the exopod very elongated, endopod high, reaching 0.9 of length of flagellum of exopod (Fig. 14 K, L ). Podobranch of second maxilliped slightly reduced, with few finger-like projections (Fig. 14 M ). Third maxilliped reaching near the end of antennular peduncle, ending in single terminal claw, exopod reaching 0.4 of length of penultimate segment; ultimate segment shorter penultimate segment; epipod present on the coxa (Fig. 14 N ). Branchial formula as is typical for genus, five pairs of pleurobranchs well developed; three pairs of arthrobranchs, two on third maxillipeds, with second pair strongly reduced in size, one pair on first pereiopod; one pair of podobranchs on second maxillipeds slightly reduced.

Pereiopods. Epipods present on first to fourth pereiopods. First pereiopod short, robust, reaching beyond end of basal segment of antennular peduncle; chela 2.03–2.35 (median 2.11) × as long as wide, 1.37–1.5 (median 1.4) × length of carpus; tips of fingers rounded, with hook; dactylus shorter than palm, 0.82–0.9 (median 0.88) × as long as palm; carpus excavated strongly anteriorly, 1.5–1.75 (median 1.65) × as long as wide; carpus 0.8–1.0 (median 0.9) × length of merus; merus 2.39–2.67 (median 2.47) × as long as wide, longer than ischium (Fig. 15 A ). Second pereiopod long, slender, reaching to distal end of antennular peduncle; chela 3.16–3.5 (median 3.28) × as long as wide, 0.64–0.71 (median 0.67) × length of carpus; tips of fingers rounded, without hook; dactylus 1.33–1.64 (median 1.52) × as long as palm; carpus 6.07–7.08 (median 6.57) × as long as wide, 1.02–1.12 (median 1.11) × as long as merus; merus 5.92–6.38 (median 6.33) × as long as wide, longer than ischium (Fig. 15 B ). Third pereiopod slender, reaching beyond end of scaphocerite by its dactylus, terminating in one claw, with four or five accessory spiniform setae on flexor margin, dactylus 3.0–3.83 (median 3.64) × as long as wide (terminal claw and spiniform setae on flexor margin included), propodus 8.5–9.75 (median 9.0) × as long as wide, 3.48–3.950 (median 3.86) × as long as dactylus; carpus 4.69–4.83 (median 4.77) × as long as wide, 0.67–0.76 (median 0.72) × as long as propodus, 0.52–0.58 (median 0.53) × as long as merus; merus 5.63–6.59 (median 6.05) × as long as wide, bearing 3 strong, movable spiniform setae on posterior margin of outer surface; ischium without movable spiniform seta (Fig. 15 C, D ). Fifth pereiopod slender, reaching to end of second segment of antennular peduncle, dactylus 2.67–3.38 (median 3.13) × as long as wide (terminal claw and spiniform setae on flexor margin included), terminating in one large claw, with 37–39 spiniform setae on flexor margin; propodus 11.25–13.14 (median 11.5) × as long as wide, 3.41–3.91 (median 3.75) × length of dactylus; carpus 4.73–5.0 (median 5.0) × as long as wide, 0.56–0.6 (median 0.58) × as long as propodus, 0.63–0.71 (median 0.67) × as long as merus; merus 5.5–6.33 (median 6.31) × as long as wide, bearing 3 strong, movable spiniform setae on posterior margin of outer surface, ischium without movable spiniform setae (Fig. 15 E, F ).

Pleopods. Endopod of male first pleopod extending to 0.87 of exopod, sub-rectangular in shape, anterior part not folded backwards, 3.15–3.35 (median 3.19) × as long as proximal width, inner margin concave, outer margin slightly convex, rounded distally, long simple setae on outer and distal margins, medium-length setae on inner margin; with appendix interna curved upwards, not or slightly exceeding terminal margin of endopod by 0.23 of its length (Fig. 15 G, H ). Appendix masculina of male second pleopod slender, reaching to proximal 0.8 of endopod length, 7.3 × as long as distal width, stick-shaped, with some spiniform setae on outer surface and on distal surface; appendix interna at the middle of appendix masculina, narrow, small, extending ~ 0.54 length of appendix masculina (Fig. 15 I, J ).

Coloration.

The body is slightly yellowish to dark blue in color, with many black spots of irregular sizes (Fig. 16 A, B ).

Reproductive biology.

Four ovigerous females, ZMB 33814, cl 5.0 mm, undeveloped eggs 1.1 × 0.7 mm, cl 5.5 mm, eggs with eyespots 1.1 mm × 0.8 mm.

Variation.

There are variations between the populations of the new species on the length of the rostrum, stylocerite, and number of teeth on rostrum. In general, compared to the specimens from the type locality and the nearby locality (ca 3 km, ZMB 32923) with the specimens from ZMB 33814, ZMB 33793, and ZMB 33788 they showed shorter rostrum (can reach only to the end of the basal segment of antennular peduncle vs reaching to the middle of the second segment of the antennular peduncle), lower number of teeth on the rostrum dorsal (up to 8 teeth vs up to 12 teeth) and shorter stylocerite (reaching to the end of the basal segment of the antennular peduncle vs reaching to the beginning of the second segment).

Etymology.

The new species is named after the type locality, Tam Kim Commune. The name is used as a noun in apposition.

Habitat.

This new species was found in small streams and pools running through the forest. The substratum includes sand, gravel, and bedrock in a water depth of 0.2–0.4 m (Fig. 17 ).

Distribution.

This species is only distributed in Nguyen Binh District, Cao Bang Province in the high elevation from 500 m to 800 m. The estimated area of occupancy is less than 1000 km 2.

Molecular phylogenetic results.

Caridina tamkim sp. nov. is well supported as the sister group a clade comprising C. namdat , C. pacbo and C. pseudoserrata . (Fig. 18 ). The minimum genetic divergence (p-distance) to a species within that clade ( C. namdat ) is 9.5 % (COI) and 3.9 % (16 S), respectively (Suppl. materials 1, 2).

Remarks.

Caridina tamkim , new species, looks similar to C. pacbo in the shape of the rostrum and the male first pleopod ( Do et al. 2020). However, it can be distinguished by a suite of characteristics: the lower number of teeth in the rostrum (0–8 + 0 – 4 / 0 – 2 vs 5–12 + 2 – 6 / 0 – 3); stylocerite extending (mostly reaching to end of basal segment, sometimes to the beginning of second segment vs reaching to the middle of the second segment of the antennular peduncle); slender merus of the first pereiopod (2.39–2.67 × as long as wide vs 2.75–3.8 × as long as wide); slender chela and merus of second pereiopod (3.16–3.5 × as long as wide vs 2.67–3.09 × as long as wide, 5.92–6.38 × as long as wide vs 5.0–5.86 × as long as wide, respectively); the distal margins of the endopod of the male first pleopod (slightly extended on both left and right sides vs not extended) (Figs 14 A, B , 15 A, B, G, H ; cf. Do et al. 2020: figs 5 A, B, 6 A, B, G, H).

Figures

Figure 14. Caridina tamkim sp. nov. adult male, cl 5.2 mm (ZMB 32924). A. Cephalothorax and cephalic appendages, lateral view; B. Antennular peduncle; C. Scaphocerite; D. Telson; E. Distal portion of telson; F. Preanal carina; G. Uropodal diaeresis; H. Mandible; I. Maxillula; J. Maxilla; K. First maxilliped; L. Distal end of palp of first maxilliped; M. Second maxilliped; N. Third maxilliped. Scale bars: 1 mm (A); 0.5 mm (B – D); 0.2 mm (E – K, M, N); 0.1 mm (L).

Figure 15. Caridina tamkim sp. nov. adult male, cl 5.2 mm (ZMB 32924). A. First pereiopod; B. Second pereiopod; C. Third pereiopod; D. The same, dactylus; E. Fifth pereiopod; F. The same, dactylus; G. Male first pleopod; H. Endopod of male first pleopod; I. Male second pleopod; J. Appendix masculina and interna of male second pleopod. Scale bars: 1 mm (A, B, C, F, G, I); 0.2 mm (D, E, H, J).

Figure 16. Live coloration of Caridina tamkim sp. nov. A. ZMB 32924; B. ZMB 33814, collected in Cao Bang Province, Vietnam.

Figure 17. Habitat of Caridina tamkim sp. nov. (ZMB 33814) in Cao Bang Province, Vietnam.

Figure 18. Bayesian Inference phylogram showing the relationships of the four new species of Caridina to other Vietnamese atyids, based on the analysis of two mitochondrial gene fragments. Numbers on branches show Bayesian posterior probabilities (> 0.7) and ML bootstrap values (> 70). An asterisk (*) indicates nodes with full support (1 / 100) in both analyses. The scale bar indicates the substitution rate. Numbers in brackets give the DNA accession number at MfN (MfN DNA Crust). See Table 1 for information on the sequenced specimens.