Caridina caii Hou, Zhang & Guo, 2025

Hou, Junjie, Zhang, Jiping, Chen, Bing, Zhang, Yixuan, Chen, Wenjian & Guo, Zhaoliang, 2025, Integrative taxonomy reveals the Caridina clinata Cai, Nguyen & Ng, 1999 species complex (Crustacea, Decapoda, Atyidae), with descriptions of eight new species from Hainan Island, China, Zoosystematics and Evolution 101 (4), pp. 2295-2336 : 2295-2336

publication ID	https://doi.org/10.3897/zse.101.172207
publication LSID	lsid:zoobank.org:pub:55065651-D7CD-46B2-AB9E-B53611DD38A5
DOI	https://doi.org/10.5281/zenodo.17651794
persistent identifier	https://treatment.plazi.org/id/DCE005D8-42CD-5224-88F6-083314BEB6E2
treatment provided by	Zoosystematics and Evolution by Pensoft
scientific name	Caridina caii Hou, Zhang & Guo
status	sp. nov.

Treatment

Caridina caii Hou, Zhang & Guo sp. nov.

Figs 2 B View Figure 2 , 5 View Figure 5 , 6 View Figure 6

Caridina clinata Cai, 2014: 207–231, Figs 10, 11. View in CoL

Materials examined.

China – Hainan Island • Holotype: 1 ♂, cl 4.3 mm, ( FU 5722001 ), Wuzhishan City , 18°54'15"N, 109°37'33"E, al. 643 m, stn. 4, coll. WANG C. Y. and HOU J. J., 28 Jan. 2024 GoogleMaps .

Paratypes: 1 ♂, cl 4.1 mm, ( FU 5722002 ); 1 ♂, cl 4.2 mm, ( FU 5722003 ); 1 ♂, cl 4.0 mm, ( FU 5722005 ); 1 ♀, cl 4.7 mm, ( FU 5722004 ); 1 ♀, cl 3.8 mm, ( FU 5722006 ); 2 ♀♀, cl 4.2–4.6 mm, ( FU 5722007 ); 1 ovigerous ♀, cl 4.9 mm, ( FU 5722008 ), same collection data as holotype GoogleMaps .

Comparative material.

Caridina lanceifrons Yu, 1936 . China – Hainan Island • 3 ♂♂, cl 3.8–4.9 mm, ( FU 5727023 ); 3 ♀♀, cl 5.2–6.1 mm, ( FU 5727024 ), Qiongzhong County, 19°1'26"N, 109°50'27"E, al. 312 m, stn. 6, coll. WANG C Y and HOU J J, 23 Jan 2024. Caridina minnanica Liang, 2002 . China GoogleMaps – Guangdong Prov. • 1 ♂, cl 3.1 mm, ( FU 5290001 ), Jiangmen City, coll. Wen, 28 Feb 2025. 2 ♀♀, cl 5.6–6.1 mm, ( FU 5166001 ), Shanwei City , coll. ZHU, 8 Jul. 2025.

Description.

Body (Fig. 2 B View Figure 2 ): Males up to 4.3 mm cl, females up to 4.9 mm cl. Sixth abdominal somite 0.49–0.55 times as long as carapace.

Rostrum (Fig. 5 A View Figure 5 ): Short, reaching to the end of the second segment of antennular peduncle, sloping ventral anteriorly; 0.4–0.5 of cl; armed dorsally with 11–16 teeth, including 3–5 on carapace posterior to orbital margin, ventrally with 1–3 teeth; rostral formula 3–5 + 8 – 11 / 1 – 3; lateral carina dividing rostrum into two unequal parts, continuing posteriorly to orbital margin.

Eyes (Fig. 5 A View Figure 5 ): Well-developed, on short ocular peduncle, cornea globular.

Carapace (Fig. 5 A View Figure 5 ): Smooth, glabrous; antennal spine acute, fused with inferior orbital angle; pterygostomian margin broadly rectangular, slightly produced forward; pterygostomian spine absent.

Antennule (Fig. 5 B View Figure 5 ): Stylocerite reaching 0.75–0.89 times as long as basal segment of antennular peduncle; basal segment shorter or as long as combined length of second and third segments, 1.61–1.92 times as long as second segment; second segment 1.16–1.31 times as long as third segments; all segments with marginal plumose setae.

Antenna (Fig. 5 C View Figure 5 ): Scaphocerite 3.3 times as long as wide, outer margin straight, asetose, ending in a strong sub-apical spine, inner and anterior margins with long plumose setae.

First maxilliped (Fig. 5 G View Figure 5 ): Palp of first maxilliped broadly triangular, ending in finger-like projection.

Third maxilliped (Fig. 6 B View Figure 6 ): Basal segment as long as penultimate segment; penultimate segment 1.01–1.11 times as long as distal segment, ending in a large claw-like spine surrounded by simple setae, preceded by 4–5 thin spines on distal third of posterior margin, proximally a clump of long and short simple, serrate setae; exopod reaching beyond the middle of second segment, distal margin with long plumose setae.

First pereiopod (Fig. 6 C View Figure 6 ): Chela 2.01–2.29 times as long as high, 1.32–1.69 times length of carpus; movable finger 3.00–3.63 times as long as wide and 0.96–1.33 times as long as palm, setal brushes well-developed; carpus 1.37–1.73 times as long as wide, slightly excavated distally; merus 0.91–1.29 times as long as carpus.

Second pereiopod (Fig. 6 D View Figure 6 ): Chela 2.68–2.95 times as long as high, 0.86–0.88 times as long as carpus; movable finger 3.62–4.10 times as long as wide and 1.47–1.93 times as long as palm, setal brushes well-developed; carpus 4.30–4.44 times as long as wide, slightly excavated distally; merus 0.91–1.01 times as long as carpus.

Third pereiopod (Fig. 6 E View Figure 6 ): Dactylus 3.21–4.28 times as long as wide, terminating in a prominent claw-like spine surrounded by simple setae, followed by 5 spiniform setae; propodus 3.60–4.28 times as long as dactylus, 9.06–11.12 times as long as wide; carpus 0.65–0.69 times as long as propodus; merus 1.87–2.07 times as long as carpus, with 4 spiniform setae on the posterior margin. Ischium sometimes with 1 small movable spiniform setae on the posterior margin.

Fourth pereiopod: Proportion and spination similar to third pereiopod.

Fifth pereiopod (Fig. 6 F View Figure 6 ): Dactylus 3.10–4.28 times as long as wide, ending in prominent claw-like spine surrounded by simple setae, followed by a row of 25–29 spiniform setae; propodus 3.82–4.94 times as long as dactylus, 11.22–13.56 times as long as wide; carpus 0.53–0.55 times as long as propodus; merus 1.53–1.57 times as long as carpus, with 3–4 spiniform setae on the posterior margin.

First four pereiopods with epipod.

First pleopod (Fig. 6 G, H View Figure 6 ): Endopod of male first pleopod subtriangular, 0.34–0.38 times as long as exopod, 2.27–2.44 times as long as wide; appendix interna well developed, arising from distal 0.33 of endopod, reaching slightly beyond the end of endopod, distally with cincinuli.

Second pleopod (Fig. 6 I View Figure 6 ): Appendix masculina club-shaped, reaching 0.57–0.64 length of exopod, inner margin and tip bearing nearly equal long and stout spiniform setae; appendix interna well developed, reaching 0.25 length of appendix masculina, distally with cincinuli.

Telson (Fig. 6 J View Figure 6 ): Tapering posterior, with a projection, with 5 pairs of short spiniform setae dorsally and one pair of short spiniform setae dorsolaterally; posterior margin with 4 pairs of intermedial spiniform setae. Exopodite of the uropod (Fig. 6 K View Figure 6 ) bears a series of 16–18 movable spinules along diaresis.

Eggs: 0.57–0.62 mm × 0.98–1.02 mm in diameter.

Remarks.

Based on morphological and molecular analyses of specimens from Wuzhishan (the same locality studied by Cai) compared with topotype specimens of Caridina clinata from Vietnam, our findings reveal distinct differences between the Wuzhishan population and C. clinata , demonstrating that its initial identification as C. clinata by Cai (2014) was incorrect. The Wuzhishan population represents a new species, formally described as Caridina caii sp. nov. It can be distinguished from C. clinata by the following key features: the different shape and proportion of the endopod of the male first pleopod (subtriangular with pointed tip, 0.34–0.38 times as long as exopod, 2.27–2.44 times as long as wide vs. oblong-reniform with rounded tip, 0.46–0.67 times as long as exopod, 2.40–3.04 times as long as wide in C. clinata ); the broader carpus of second pereiopod (carpus 4.30–4.44 times as long as wide vs. carpus 4.70–6.30 times in C. clinata ); fewer spiniform setae on the flexor margin of the dactylus of the fifth pereiopod (25–29 spiniform setae vs. 41–51 spiniform setae in C. clinata ); and smaller eggs (0.57–0.62 × 0.98–1.02 mm vs. 0.60–0.75 × 1.10–1.15 mm in C. clinata ).

At first glance, Caridina caii sp. nov. closely resembles C. minnanica Liang, 2002 . However, it can be differentiated from the latter by the shorter rostrum (reaching only to the end of the second segment of the antennular peduncle vs. to the end of the antennular peduncle in C. minnanica ) and with fewer ventral teeth (1–3 teeth vs. 4–8 teeth in C. minnanica ); the palp of the first maxilliped with a long finger-like projection (vs. absent in C. minnanica ); and the shorter carpus of the second pereiopod (4.30–4.44 times as long as wide vs. 5.60–6.20 times in C. minnanica ).

Cai (2014) noted that the Wuzhishan population morphologically resembles Caridina lanceifrons and provided an in-depth comparison between these two taxa. Our study supports Cai’s conclusion that C. caii sp. nov. is morphologically distinct from C. lanceifrons . Our phylogeny suggests that C. caii sp. nov. clusters with C. lanceifrons but is not closely related to C. clinata .

Molecular results.

The intraspecific p-distances of COI of the new species were 0.6 % – 2.5 %. The new species is most similar in genetic divergence (p-distance) to C. lanceifrons (4.0 % – 6.7 %) and C. minnanica (7.5 % – 9.6 %). According to molecular analysis, the distance between the new species and C. clinata is 25.4 % – 29.3 %. The intraspecific p-distances of 16 SrRNA of the new species were 0 % – 0.9 %. The new species is most similar in genetic divergence (p-distance) to C. lanceifrons (2.0 % – 3.1 %) and C. minnanica (2.5 % – 3.6 %). According to molecular analysis, the distance between the new species and C. clinata is 10.8 % – 12.1 % (Fig. 21 View Figure 21 , Suppl. materials 1, 2).

Coloration.

When alive, the body of shrimp dense with many gray small pigment dots (Fig. 2 B View Figure 2 ).

Etymology.

Caridina caii is dedicated to Cai Y. X., who not only discovered the species but also made outstanding contributions to carcinology.

Ecological notes.

C. caii sp. nov. was collected from site 4. At site 4, the stream measured 1.0–2.0 m in width and 0.5–1.0 m in depth, and its substrate consisted of gravel, sand, and leaf litter. The shrimps lived densely among leaf litter, exhibiting high population density. The stream water was Intermediately flowing (Fig. 2 B View Figure 2 , Table 1 View Table 1 ).

Distribution.

Only occurring in Wuzhishan City, Hainan Island.