Caridina tanson, 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 tanson sp. nov.

Figs 10 , 11 , 12

Type material.

Holotype. • Adult male, cl 4.5 mm, IB -FS 009 , Vietnam, Phu Tho Province, Tan Son District, Xuan Son Commune, Ban Lap Village , a small stream, 21°8'40.09"N, 104°56'40.739"E, 28 July 2022, collected by Thi Yen Phan . Paratypes. • 6 females, cl 4.0–6.0 mm, 10 males, cl 4.0–6.0 mm, ZMB 32979 , same data as holotype ; • male, cl 4.5 mm, ZMB 30729 , Vietnam, Phu Tho Province, Tan Son District, Dong Son Commune, Than stream, site 2 , 21°11'15.4"N, 104°52'22.9"E, 29 August 2013, collected by Tran Anh Duc .

Comparative material.

Caridina pseudoserrata Dang & Do, 2007 , • adult male, cl 4.5 mm, ZMB 31570 , Vietnam, Cao Bang Province, Phuc Hoa District, My Hung Commune, Na Rieng village , a stream runs inside Nguom Khuoi Khua Cave , 22°29'10.8"N, 106°33'3.27"E, 27 May 2017, collected by Van Tu Do.

Diagnosis.

This new species is characterized by rostrum short, straight, slender, tapering towards tip, reaching from beginning to end of third segment of antennular peduncle (Fig. 10 A ); stylocerite reaches from beginning to 0.2 × length of second segment of the antennular peduncle (Fig. 10 B ); carpus of fifth pereiopod slender, 7.3 × as long as wide (Fig. 11 A ); endopod of male first pleopod kidney-shaped, extending to 0.52 of exopod, 2.4 × as long as proximal width (Fig. 11 G, H ).

Description.

Cephalothorax and cephalic appendages. Carapace length 4.0– 6.4 mm (median 4.5 mm, n = 11). Rostrum slender, straight, reaching to beginning, sometime to the end of the third segment of antennular peduncle to distal end of antennular peduncle, 0.45–0.75 (median 0.52) as long as carapace, rostral formula 4–6 + 9 – 14 / 2 – 5 (Fig. 10 A ). Suborbital angle acute, completely fused with antennal spine; pterygostomian margin rounded, slightly produced forward (Fig. 10 A ). Eyes well developed with globular cornea, anterior end reaching to 0.7 length of basal segment of antennular peduncle (Fig. 10 A ). Antennular peduncle 0.46–0.67 (median 0.56) as long as carapace; basal segment 1.0–1.67 (median 1.25) × as long as second segment, second segment 1.14–2 (median 1.58) × as long as third segment (Fig. 10 B ). Stylocerite reaching to beginning or to 0.2 of length of second segment of antennular peduncle (Fig. 10 B ). Scaphocerite ovate, reaching beyond distal end of antennular peduncle, 3–3.81 (median 3.37) × as long as wide (Fig. 10 A, C ).

Abdominal somites, telson, and uropods. Sixth abdominal somite 0.33–0.5 (median 0.4) length of carapace, 1.36–1.73 (median 1.5) × as long as fifth abdominal somite, 0.62–0.95 (median 0.76) length of telson. Telson length 2.0–2.89 (median 2.5) × as long as proximal wide, distal margin triangular, terminating in a short median projection, with 5–6 pairs of dorsal spiniform setae and one pair of dorso-subdistal spiniform setae; distal end with 4–5 pairs of spiniform setae, lateral pair longer than intermediate pairs (Fig. 10 D, E ). Preanal carina low, slightly bent backwards, with few setae, lacking a spine (Fig. 10 F ). Uropodal diaeresis with 16–21 (median 18) movable spiniform setae, outermost shorter than lateral angle (Fig. 10 G ).

Mouthparts and branchiae. Incisor process of mandible ending in one row of 6–7 irregular teeth, molar process truncated (Fig. 10 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. 11 I ). Upper endites of maxilla subdivided, palp short, scaphognathite tapering posteriorly, with numerous long, curved setae at posterior margin (Fig. 10 J ). Distal end of palp of first maxilliped triangular, with a short projection; flagellum of the exopod very elongated, endopod high, reaching 0.8 length of flagellum of exopod (Fig. 10 K, L ). Podobranch of second maxilliped slightly reduced, with few finger-like projections (Fig. 10 M ). Third maxilliped reaching to end of antennular peduncle, ending in single terminal claw, exopod reaching 0.4 length of penultimate segment; ultimate segment slightly longer than penultimate segment; epipod present on the coxa (Fig. 10 N ). Branchial formula as typical for Paracaridina genus, five pairs of pleurobranchs well developed; two pairs of arthrobranchs on third maxillipeds, with second pair strongly reduced in size; podobranch on second maxillipeds slightly reduced, arthrobranch on first pereiopod absent ( Liang et al. 1999).

Pereiopods. Epipods present on first to fourth pereiopods. First pereiopod short, robust, reaching end of basal segment of antennular peduncle; chela 1.91–2.75 (median 2.28) × as long as wide, 1.17–1.69 (median 1.41) × length of carpus; tips of fingers rounded, without hook; dactylus 0.77–1.18 (median 0.97) × as long as palm; carpus excavated strongly anteriorly, 1.6–2.29 (median 2.0) × as long as wide; carpus 0.79–1.0 (median 0.84) × length of merus; merus 2.5–3.6 (median 3.0) × as long as wide, longer than ischium (Fig. 11 A ). Second pereiopod long, slender, reaching beyond distal end of antennular peduncle; chela 2.11–3.63 (median 2.75) × as long as wide, 0.63–0.87 (median 0.76) × length of carpus; tips of fingers rounded, without hook; dactylus 0.92–1.4 (median 1.29) × as long as palm; carpus 4.6–6.0 (median 5.0) × as long as wide, 0.74–1.17 (median 1.0) × as long as merus; merus 4.8–7 (median 5.8) × as long as wide, longer than ischium (Fig. 11 B ). Third pereiopod slender, reaching beyond distal end of antennular peduncle by its dactylus, terminating in one claw, with five to six accessory spiniform setae on flexor margin, dactylus 2.67–4.0 (median 3.0) × as long as wide (terminal claw and spiniform setae on flexor margin included), propodus 9.75–12 (median 10.13) × as long as wide, 3.89–5.13 (median 4.44) × as long as dactylus; carpus 4–5.5 (median 4.5) × as long as wide, 0.49–0.69 (median 0.6) × as long as propodus, 0.43–0.56 (median 0.47) × as long as merus; merus 5.63–7.86 (median 7.01) × as long as wide, bearing three strong, movable spiniform setae on posterior margin of outer surface; ischium with one small movable spiniform seta (Fig. 11 C, D ). Fifth pereiopod slender, reaching to end of third segment of antennular peduncle, dactylus 3.67–7 (median 4.17) × as long as wide (terminal claw and spiniform setae on flexor margin included), terminating in one large claw, with 41–58 spiniform setae on flexor margin; propodus 10.75–14.67 (median 12.38) × as long as wide, 3.31–4.82 (median 4.01) × length of dactylus; carpus 4.17–6.25 (median 5) × as long as wide, 0.42–0.54 (median 0.48) × as long as propodus, 0.49–0.71 (median 0.58) × as long as merus; merus 6.5–8.6 (median 7.3) × as long as wide, bearing 3 strong, movable spiniform setae on posterior margin of outer surface, ischium without movable spiniform setae (Fig. 11 E, F ).

Pleopods. Endopod of male first pleopod extending to 0.52 of exopod, elongated and kidney-shaped, 2.14–2.57 (median 2.43) × as long as proximal width, inner margin concave, outer margin slightly convex, rounded distally, long pappose setae on outer and distal margins, medium-length setae on inner margin; appendix interna long, exceeding terminal margin of endopod by 0.43 its length (Fig. 11 G, H ). Appendix masculina of male second pleopod slender, reaching to proximal 0.63 endopod length, 6.73 × as long as distal width, stick-shaped, with some short spiniform setae on outer surface and some long spiniform setae on distal surface; appendix interna at the middle of appendix masculina, small, extending ~ 0.66 length of appendix masculina (Fig. 11 I, J ).

Coloration.

The body is slightly yellowish to dark blue in color, with many small reddish spots and small lines of irregular sizes (Fig. 12 A, B ).

Reproductive biology.

Ovigerous female, ZMB 32979, cl 6.0 mm, eggs with eyespots 1.1 × 0.7 mm.

Etymology.

The new species is named after the type locality, Tan Son District. The name is used as a noun in apposition.

Habitat.

This new species was found in small streams. The substratum includes sand, gravel, bedrock, rotten leaves, and organic mulch in a water depth of 0.2–0.5 m (Fig. 13 ).

Distribution.

This species has only been recorded in the highland streams of Tan Son District, Phu Tho Province at altitudes from 200 m to 500 m. The estimated area of occupancy is less than 1000 km 2.

Molecular phylogenetic results.

Caridina tanson sp. nov. is well supported as the sister group a clade comprising C. haivanensis , C. clinata and C. xuanlien sp. nov. (Fig. 18 ). The minimum genetic divergence (p-distance) to a species within that clade is 10.0 % (COI, C. haivanensis ) and 4.1 % (16 S, C. clinata ), respectively (Suppl. materials 1, 2).

Remarks.

Caridina tanson , new species, is similar to C. pseudoserrata , also from northeast Vietnam, in the shape of the rostrum and endopod of male first pleopod ( Dang and Do 2007 a). The new species can be distinguished from C. pseudoserrata by a suite of characteristics: shorter stylocerite (reaching to the beginning or to 0.2 the length of the second segment of antennular peduncle vs reaching to 0.4–0.5 of second segment of antennular peduncle); shorter endopod of male first pleopod (2.4 × as long as proximal width vs 2.77 × as long as proximal width); longer appendix interna of endopod of male first pleopod (exceeding terminal margin of endopod by 0.43 its length vs not exceeding or just slightly exceeding the terminal margin of endopod) (Fig. 10 A, B , 11 G, H ; cf. Dang and Do 2007 a: figs 1 A, 2 A, B).

Caridina tanson sp. nov. is also close to C. xuanlien sp. nov. in the shape of the rostrum and endopod of the male first pleopod. However, C. tanson can be distinguished from C. xuanlien sp. nov. by: there are more teeth on the rostrum, armed with 9–14 dorsal teeth on the rostrum anterior to the orbital margin and 2–5 ventral teeth (vs 3–9 dorsal teeth on the rostrum anterior to the orbital margin and 0–2 ventral teeth); the endopod of the male first pleopod is stouter, 2.43 × as long as proximal width (vs 2.79 × as long as proximal width); appendix interna of endopod of male first pleopod is longer, exceeding terminal margins of endopod by 0.43 of its length (vs exceeding terminal margins of endopod by 0.23 of its length); appendix masculina of male second pleopod is stouter, 6.73 × as long as distal width (vs 8.25 × as long as distal width).

Figures

Figure 10. Caridina tanson sp. nov. adult male, cl 4.8 mm (ZMB 32979). 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 – J).

Figure 11. Caridina tanson sp. nov. adult male, cl 4.8 mm (ZMB 32979). 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 12. A, B. Live coloration of Caridina tanson sp. nov. (ZMB 32979), collected in Phu Tho Province, Vietnam.

Figure 13. Collecting the samples in the habitat of Caridina tanson sp. nov. (ZMB 32979) in Phu Tho 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.