Caridina ngocson, 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

publication ID	https://doi.org/10.3897/zookeys.1247.148607
publication LSID	lsid:zoobank.org:pub:8219660E-6CA5-46DA-8CE6-665C81338740
DOI	https://doi.org/10.5281/zenodo.16533228
persistent identifier	https://treatment.plazi.org/id/9F18B6F6-A355-5E5F-B488-68BB80DC570C
treatment provided by	ZooKeys by Pensoft
scientific name	Caridina ngocson
status	sp. nov.

Treatment

Caridina ngocson sp. nov.

Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4

Type material.

Holotype. • Adult male, cl 4.6 mm, IB -FS 007 , Vietnam, Hoa Binh Province, Lac Son District, Ngoc Son Commune, Van Village , a small stream, 20°27'55.721"N, 105°18'8.027"E, 23 March 2017, collected by Van Tu Do GoogleMaps . Paratypes. • 7 males, cl 3.8–5.3 mm, 4 females, cl 4.2–5.3 mm, 50 additional specimens, ZMB 30276 View Materials , same data as holotype GoogleMaps ; • male, cl 4.4, female, cl 5 mm, IB -FS 008 , Vietnam, Hoa Binh Province, Lac Son District, Ngoc Son Commune , a small stream, 20°24'11.92"N, 105°22'23.5"E, collected by Thi Yen Phan, 02 February 2023 GoogleMaps .

Comparative material.

Caridina serrata Stimpson, 1860 . • 10 males, cl 3.1–4.7, 5 females, cl 4.0–4.6, ZMB 30306 View Materials , Vietnam, Quang Nam Province, Hoi An City, Cu Lao Cham Island GoogleMaps , a small stream running into the reservoir, 15°56'34.9"N 108°31'22.7"E, collected by Pham The Cuong, 10 May 2017.

Diagnosis.

Caridina ngocson sp. nov. can be distinguished from other members of the genus Caridina by a combination of the following characteristics: short, slender, and slightly downward-curving rostrum, reaching from beginning to middle of second segment of antennular peduncle (Fig. 2 A View Figure 2 ); stylocerite extending beyond distal end of basal antennular peduncle; rostral formula of 4–6 + 5 – 11 / 0 – 2; well-developed eyes (Fig. 2 B View Figure 2 ); kidney-shaped endopod of male first pleopod, with appendix interna slightly exceeding terminal margin of endopod by 0.23 of its length (Fig. 3 G, H View Figure 3 ); appendix masculina of male second pleopod slender, reaching approximately 0.43 × endopod length; appendix interna extending ~ 0.60 × length of appendix masculina (Fig. 3 I, J View Figure 3 ); and large eggs.

Description.

Cephalothorax and cephalic appendages. Carapace length 3.8–5.3 mm (median 4.4 mm, n = 12). Rostrum short and slender, straight, reaching to beginning to middle of second segment of antennular peduncle, 0.25–0.4 (median 0.33) × as long as carapace, rostral formula 4–6 + 5 – 11 / 0 – 2 (Fig. 2 A View Figure 2 ). Suborbital angle acute, completely fused with antennal spine; pterygostomian margin rounded, slightly introduced forward (Fig. 2 A View Figure 2 ). Eyes well developed with globular cornea, anterior end reaching to 0.8 × length of basal segment of antennular peduncle (Fig. 2 A View Figure 2 ). Antennular peduncle 0.47–0.58 (median 0.54) × as long as carapace; basal segment 1.98–2.39 (median 2.05) × as long as second segment, second segment 0.96–1.24 (median 1.05) × as long as third segment (Fig. 2 B View Figure 2 ). Stylocerite reaching to beginning or to 0.4 × length of second segment of antennular peduncle (Fig. 2 B View Figure 2 ). Scaphocerite ovate, reaching beyond distal end of antennular peduncle, 2.55–2.97 (median 2.55) × as long as wide (Fig. 2 A, C View Figure 2 ).

Abdominal somites, telson, and uropods. Sixth abdominal somite 0.36–0.4 (median 0.38) × length of carapace, 1.36–1.69 (median 1.45) × as long as fifth abdominal somite, 0.64–0.84 (median 0.73) × length of telson. Telson length 2.14–2.55 (median 2.27) × as long as proximal wide, distal margin triangular, terminating in a short median projection, with 4–6 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 longer than intermediate pairs (Fig. 2 D, E View Figure 2 ). Preanal carina low, slightly bent backwards, with few setae, lacking a spine (Fig. 2 F View Figure 2 ). Uropodal diaeresis with 16–21 (median 20) movable spiniform setae, outermost longer than lateral angle (Fig. 2 G View Figure 2 ).

Mouthparts and branchiae. Incisor process of mandible ending in one row of 5–7 irregular teeth, molar process truncated (Fig. 2 H View Figure 2 ). 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. 2 I View Figure 2 ). Upper endites of maxilla subdivided, palp short, scaphognathite tapering posteriorly, with numerous long, curved setae at posterior margin (Fig. 2 J View Figure 2 ). 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. 2 K, L View Figure 2 ). Podobranch of second maxilliped slightly reduced, with few finger-like projections (Fig. 2 M View Figure 2 ). Third maxilliped reaching to end of antennular peduncle, ending in single terminal claw, exopod reaching 0.6 × length of penultimate segment; ultimate segment longer than penultimate segment; epipod present on the coxa (Fig. 2 N View Figure 2 ). Branchial formula as typical for genus Paracaridina Liang, Guo & Tang, 1999 , five pairs of pleurobranchs well developed; two pairs of arthrobranchs on third maxillipeds, with second pair strongly reduced in size; one pair of podobranchs on second maxilliped slightly reduced, arthrobranch on first pereiopod absent ( Liang et al. 1999).

Pereiopods. Epipods present on first fourth pereiopods. First pereiopod short, robust, reaching end of basal segment of antennular peduncle; chela 1.91–2.22 (median 2.02) × as long as wide, 1.22–1.44 (median 1.26) × length of carpus; tips of fingers rounded, without hook; dactylus 0.73–0.89 (median 0.83) × as long as palm; carpus excavated strongly anteriorly, 1.73–2.25 (median 1.89) × as long as wide; carpus 0.83–1.01 (median 0.95) × length of merus; merus 2.3–2.94 (median 2.67) × as long as wide, longer than ischium (Fig. 3 A View Figure 3 ). Second pereiopod long, slender, reaching beyond distal end of antennular peduncle; chela 2.19–2.62 (median 2.4) × as long as wide, 0.60–0.78 (median 0.69) × length of carpus; tips of fingers rounded, without hook; dactylus 1.04–1.4 (median 1.17) × as long as palm; carpus 5.0–5.69 (median 5.16) × as long as wide, 0.93–1.05 (median 1.0) × as long as merus; merus 4.81–5.58 (median 5.12) × as long as wide, longer than ischium (Fig. 3 B View Figure 3 ). Third pereiopod slender, reaching beyond distal end of antennular peduncle by its dactylus, terminating in one claw, with five accessory spiniform setae on flexor margin, dactylus 2.44–3.19 (median 2.82) × as long as wide (terminal claw and spiniform setae on flexor margin included), propodus 8.38–9.3 (median 8.79) × as long as wide, 4–4.64 (median 4.17) × as long as dactylus; carpus 3.41–4.41 (median 4.01) × as long as wide, 0.53–0.69 (median 0.62) × as long as propodus, 0.46–0.55 (median 0.52) × as long as merus; merus 5.33–6.68 (median 5.74) × as long as wide, bearing 3 strong, movable spiniform setae on posterior margin of outer surface; ischium with one small movable spiniform seta (Fig. 3 C, D View Figure 3 ). Fifth pereiopod slender, reaching to end of third segment of antennular peduncle, dactylus 3.27–3.67 (median 3.53) × as long as wide (terminal claw and spiniform setae on flexor margin included), terminating in one large claw, with 30–37 spiniform setae on flexor margin; propodus 9.82–12.06 (median 10.55) × as long as wide, 3.06–3.98 (median 3.54) × length of dactylus; carpus 3.45–4.39 (median 4.0) × as long as wide, 0.46–0.57 (median 0.48) × as long as propodus, 0.56–0.66 (median 0.61) × as long as merus; merus 5.4–6.21 (median 5.99) × as long as wide, bearing 3 strong, movable spiniform setae on posterior margin of outer surface, ischium without movable spiniform setae (Fig. 3 E, F View Figure 3 ).

Pleopods. Endopod of male first pleopod extending to 0.62 × exopod, elongated and kidney-shaped, 2.43–3.04 (median 2.91) × 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; with appendix interna curved upwards, exceeding terminal margin of endopod by 0.51 its length (Fig. 3 G, H View Figure 3 ). Appendix masculina of male second pleopod slender, reaching to proximal 0.62 × endopod length, 7.38 × 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, narrow, small, extending ~ 0.54 × length of appendix masculina (Fig. 3 I, J View Figure 3 ).

Coloration.

The body is grey to slightly yellowish in color, with many small reddish black spots. There are several small stripes formed by spots on the abdominal part (Fig. 4 A – C View Figure 4 ).

Reproductive biology.

One ovigerous female, ZMB 30276, cl 4.5 mm, developed eggs, with eyespots, 1.33 × 0.84 mm (15 eggs).

Etymology.

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

Habitat.

This new species was found in a stream with mixed sand, gravel, and rock substratum, and clear ﬂowing water from the forest (Fig. 5 View Figure 5 ).

Distribution.

Our unpublished survey data throughout Vietnam indicate that this species is restricted to the Ngoc Son district of Hoa Binh province. The estimated area of occupancy is less than 500 km 2. The altitude of the habitat area ranges from 200 to 700 m. The large eggs are also clearly indicative of a landlocked life cycle.

Molecular phylogenetic results.

Caridina ngocson sp. nov. is well-supported as the sister species to C. cucphuongensis (Fig. 18 View Figure 18 ). The minimum genetic divergence (p-distance) to C. cucphuongensis ) is 6.2 % (COI) and 2.7 % (16 S), respectively (Suppl. materials 1, 2).

Remarks.

Caridina ngocson sp. nov. can be included in the C. serrata group based on a short rostrum, a long stylocerite that extends beyond the distal end of the basal antennular peduncle, the presence of dorsal teeth on the carapace, and the male pleopod endopod with a distinctive appendix interna ( Cai and Ng 1999). However, C. ngocson sp. nov. differs from C. serrata in: the rostrum is longer (reaching to the beginning to middle of the second segment of antennular peduncle vs nearly reaching to or slightly exceeding the end of the basal segment of antennular peduncle); number of ventral teeth of the rostrum is smaller (0–2 vs 0–6); scaphocerite is stouter (2.6 vs 3.0 × as long as wide); endopod of male first pleopod is more slender (2.9 vs 2.5 × as long as proximal width); egg size is bigger (1.33 × 0.84 mm vs 0.9–1.0 × 0.7– 0.6 mm) (Fig. 2 A, C, G, H View Figure 2 ; cf. Cai and Ng 1999: fig. 2 A, C, K, J).

The new species somewhat resembles Caridina cucphuongensis Dang, 1980 in the shape of the male first endopod, the appendix masculine and appendix internal of the male second pleopod. However, C. ngocson sp. nov. can be separated from C. cucphuongensis by a longer rostrum, reaching to the beginning to middle of second segment of antennular peduncle (vs just overreaching eyes to beginning of second segment); higher number of teeth on the dorsal rostrum, armed with 4–6 teeth on carapace posterior to orbital margin and 5–11 teeth on rostrum anterior to orbital margin (vs 0–3 teeth on carapace posterior to orbital margin and 2–7 teeth on rostrum anterior to orbital margin); slender chela of second pereiopod, 2.4 × as long as wide (vs 2.78 × as long as wide); a longer stylocerite, reaching to beginning or to 0.4 × length of second segment of antennular peduncle (vs reaching to beginning of second segment of antennular peduncle); higher number of spiniform setae on flexor margin of the dactylus of fifth pereiopod, 30–37 (vs 24–52 spiniform setae on flexor margin) (Figs 2 A, B View Figure 2 , 3 B, F View Figure 3 ; cf. Phan et al. 2021 b: figs 2 A, B, 3 B, F).

Caridina ngocson sp. nov. and the following two new species C. xuanlien sp. nov. and C. tanson , have the defining character of Paracaridina Liang, Guo & Tang, 1999 because of their branchial formula (5 pairs of pleurobranchs well developed; 2 pairs of arthrobranchs on third maxillipeds, with second pair strongly reduced in size; 1 pair of podobranchs on second maxilliped slightly reduced, arthrobranch on first pereiopod absent). However, this character is not unique to Paracaridina ( von Rintelen et al. 2008) and genetically the new species does not cluster with Paracaridina but – albeit with weak support – rather with Neocaridina . We have thus chosen the conservative approach of tentatively assigning it to Caridina given the clear need of a taxonomic revision at the genus level for these three genera (see Do et al. 2021 b).