Caridina fontinalis 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

Caridina fontinalis Hou, Zhang & Guo sp. nov.

Figs 2 G , 15 , 16

Materials examined.

China – Hainan Island • Holotype: 1 ♂, cl 2.4 mm, ( FU 5700001 ), Haikou City , 19°55'4"N, 110°24'45"E, al. 16 m, stn. 10, coll. WANG G. Y. and HOU J. J., 17 Jan. 2025 .

Paratypes: 1 ♂, cl 2.7 mm, ( FU 5700002 ), 1 ♂, cl 2.7 mm, ( FU 5700003 ); 1 ovigerous ♀, cl 2.4 mm, ( FU 5700004 ), 1 ♀, cl 3.4 mm, ( FU 5700005 ), same collection data as holotype .

Description.

Body (Fig. 2 G ): Small, slender and sub-cylindrical, males up to 2.7 mm cl, females up to 3.4 mm cl. Sixth abdominal somite 0.44–0.48 times as long as carapace.

Rostrum (Fig. 15 A ): Straight, reaching to the end of the first segment to the end of the second segment of the antennular peduncle; 0.3–0.4 of cl; armed dorsally with 9–11 teeth, including 3–5 on carapace posterior to orbital margin, ventrally with 1 tooth; rostral formula 3–5 + 6 / 1; lateral carina dividing rostrum into two unequal parts, continuing posteriorly to orbital margin.

Eyes (Fig. 15 A ): Well-developed, on short ocular peduncle, cornea globular.

Carapace (Fig. 15 A ): Smooth, glabrous; antennal spine acute, fused with inferior orbital angle; pterygostomian margin broadly rectangular, slightly produced forward; pterygostomian spine absent.

Antennule (Fig. 15 B ): Peduncle reaching slightly short of scaphocerite; stylocerite reaching 0.76–0.96 times as long as basal segment of antennular peduncle; basal segment shorter than combined length of second and third segments, 1.70–1.77 times as long as second segment; second segment 1.35–1.66 times as long as third segments; all segments with marginal plumose setae.

Antenna (Fig. 15 C ): Scaphocerite 3.1 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. 15 G ): Palp of first maxilliped broadly triangular, ending in finger-like projection.

Third maxilliped (Fig. 16 B ): Basal segment 0.95–1.06 times as long as penultimate segment; penultimate segment 0.85–0.94 times as long as distal segment, ending in a large claw-like spine surrounded by simple setae, preceded by 5–6 thin spines on distal third of posterior margin, proximally a clump of long and short simple, serrate setae; exopod reaching beyond middle of second segment, distal margin with long plumose setae.

First pereiopod (Fig. 16 C ): Chela 1.88–2.27 times as long as high, 1.26–1.44 times as long as carpus; movable finger 2.37–3.33 times as long as wide and 0.86–0.93 times as long as palm, setal brushes well-developed; carpus 1.36–2.11 times as long as wide, slightly excavated distally; merus 0.95–1.13 times as long as carpus.

Second pereiopod (Fig. 16 D ): Chela 2.31–2.49 times as long as high, 0.78–0.84 times as long as carpus; movable finger 3.59–4.50 times as long as wide and 1.28–1.80 times as long as palm, setal brushes well developed; carpus 4.64–6.23 times as long as wide; slightly excavated distally, merus 0.81–0.92 times as long as carpus.

Third pereiopod (Fig. 16 E ): Dactylus 3.59–4.49 times as long as wide, terminating in a prominent claw-like spine surrounded by simple setae, followed by 4–6 spiniform setae; propodus 3.41–3.87 times as long as dactylus, 10.74–11.80 times as long as wide; carpus 0.67–0.68 times as long as propodus; merus 1.80–1.85 times as long as carpus, with 3–4 spiniform setae on posterior margin. Ischium sometimes with 1 spine on the posterior margin.

Fourth pereiopod: Proportion and spination similar to third pereiopod.

Fifth pereiopod (Fig. 16 F ): Dactylus 4.37–5.39 times as long as wide, ending in prominent claw-like spine surrounded by simple setae, followed by a row of 22–32 spiniform setae; propodus 3.06–3.43 times as long as dactylus, 11.62–14.91 times as long as wide; carpus 0.56–0.57 times as long as propodus; merus 1.49–1.57 times as long as carpus, with 3–5 spiniform setae on posterior margin. Ischium sometimes with 1 spine on the posterior margin.

First four pereiopods with epipod.

First pleopod (Fig. 16 G, H ): Endopod in male oblong-reniform, 0.49–0.61 times as long as exopod, 2.76–3.29 times as long as distally wide, distal end is distinctly narrower than the basal part, with a concave inner margin and a convex outer margin, long pappose setae on outer and distal margins, medium-length setae on inner margin; appendix interna well developed, arising from distal 0.25 of endopod, reaching slightly beyond end of endopod, distally with cincinuli.

Second pleopod (Fig. 16 I ): Appendix masculina rod-shaped, reaching 0.63–0.71 length of exopod, bearing sparse long spiniform setae; appendix interna well developed, reaching 0.72–0.78 length of appendix masculina, distally with cincinuli.

Telson (Fig. 16 J ): Tapering posterior, with a projection, with 3 pairs of short spiniform setae dorsally and one pair of short spiniform setae dorsolaterally; posterior margin with 3–4 pairs of intermedial spiniform setae. Exopodite of the uropod (Fig. 16 K ) bears a series of 12–16 movable spinules along diaresis.

Eggs: 0.56–0.67 mm × 0.83–0.97 mm in diameter.

Remark.

Caridina fontinalis sp. nov. is a small species occurring in cool waters and stable flow conditions. Caridina fontinalis sp. nov. and C. lanceifrons co-occur at the same sampling site and share sexual appendage morphology and egg size. Caridina fontinalis sp. nov. is easily separated from C. lanceifrons by its shorter rostrum (reaching from the end of the first segment to the middle of the second segment of the antennular peduncle vs. extending to the end of the antennular peduncle in C. lanceifrons ); fewer rostral teeth (dorsally with 9–11 teeth and ventrally with 1 tooth vs. dorsally 14–23 and ventrally 2–5 in C. lanceifrons ); broader scaphocerite (3.1 times as long as wide vs. 3.9 times in C. lanceifrons ); and slender carpus of the second pereiopod (4.64–6.23 times as long as wide vs. 3.6–4.5 times in C. lanceifrons ).

Caridina fontinalis sp. nov. is similar to C. clinata Cai et al., 1999 , but differs by: more slender endopod of first pleopod (length of endopod 2.76–3.29 times width vs. 2.40–3.04 times in C. clinata ); the spines of the appendix masculina of the second pleopod (the spines on the middle to apical regions of the appendix masculina of the second pleopod are relatively thinner vs. the spines on the middle to apical regions of the appendix masculina of the second pleopod are relatively thicker, longer, and more densely arranged in C. clinata ); fewer dorsal teeth (9–11 vs. 12–21 in C. clinata ); fewer comb-like spines on fifth pereiopod dactylus (22–32 vs. 41–51 in C. clinata ); the ventral surface of the merus on the third pereopod bears more spiniform setae (3–5 spiniform setae vs. 3 spiniform setae in C. clinata ).

Caridina fontinalis sp. nov. is similar to C. wenchangensis sp. nov., but differs by the shape of endopod of first pleopod (the distal end is distinctly narrower than the basal part, with a concave inner margin and a convex outer margin vs. the distal end is as long as the basal part, with a relatively straight inner margin in C. wenchangensis sp. nov.); the spiniform setae of the appendix masculina of the second pleopod (the spiniform setae on the middle to apical regions of the appendix masculina of the second pleopod are relatively thinner vs. the spiniform setae on the middle to apical regions of the appendix masculina of the second pleopod are relatively thicker, longer, and more densely arranged in C. wenchangensis sp. nov.); fewer dorsal teeth (armed dorsally with 9–11 teeth, ventrally with 1 tooth vs. armed dorsally with 12–15 teeth, ventrally with 2–4 teeth in C. wenchangensis sp. nov.); the ventral surface of the merus on the third pereopod bears more spiniform setae (3–5 spiniform setae vs. 3–4 spiniform setae in C. wenchangensis sp. nov.).

Molecular results.

According to the COI sequence, the intraspecific p-distances of COI of the new species were 0 % – 0.2 %. The new species is most similar in genetic divergence (p-distance) to C. tunchengensis sp. nov. (5.3 % – 5.7 %) and C. wenchangensis sp. nov. (11.2 % – 11.5 %). According to molecular analysis, the distance between the new species and C. clinata is 11.7 % – 11.9 %. According to the 16 SrRNA sequence, the intraspecific p-distances of 16 SrRNA of the new species were 0 % – 0.7 %. The new species is most similar in genetic divergence (p-distance) to C. tunchengensis sp. nov. (1.6 % – 2.7 %) and C. clinata (2.5 % – 3.6 %). According to molecular analysis, the distance between the new species and C. wenchangensis sp. nov. is 4.6 % – 5.5 % (Fig. 21 , Suppl. materials 1, 2).

Coloration.

Eyes reddish-brown; body semi-transparent; abdomen with faint black speckles (Fig. 2 G ).

Etymology.

The name originates from their type locality, referring to their habitat at the spring’s outlet, with “ fontinalis ” meaning “ spring-dweller ” in reference to their dwelling place near the water source.

Ecological notes.

C. fontinalis sp. nov. was collected from site 10. At site 10, the stream measured 0.1–0.2 m in width and 0.1 m in depth, and its substrate consisted of rock and mud. The shrimps lived among rocks, with a low population density. The spring water was slowly flowing (Fig. 2 G , Table 1 ).

Distribution.

Only occurring in the type locality, Qiongshan District, Haikou City, Hainan Island.

Figures

Figure 2. Habitats of 9 Caridina species on Hainan Island. A. C. clinata Cai et al., 1999; B. C. caii sp. nov.; C. C. wenchangensis sp. nov.; D. C. qiongzhongensis sp. nov.; E. C. huangi sp. nov.; F. C. hepingensis sp. nov.; G. C. fontinalis sp. nov.; H. C. tunchengensis sp. nov.; I. C. brevilineata sp. nov.

Figure 15. Caridina fontinalis Hou, Zhang & Guo, sp. nov. A. Holotype male (FU 5700001); B – G. Paratype female (FU 5700005): A. Cephalothorax; B. Antennular; C. Antenna; D. Mandible; E. Maxillula; F. Maxilla; G. First maxilliped.

Figure 16. Caridina fontinalis Hou, Zhang & Guo, sp. nov. A – E, J, K. Paratype female (FU 5700005); G. Holotype male (FU 5700001); H, I. Paratype male (FU 5700002): A. Second maxilliped; B. Third maxilliped; C. First pereiopod; D. Second pereiopod; E. Third pereiopod; F. Fifth pereiopod; G, H. First pleopod of the male; I. Second pleopod of the male; J. Telson; K. Uropodal diaeresis.

Figure 21. Maximum likelihood method (ML) tree of 8 new species of Caridina and other atyids and 1 Macrobrachium species, based on the analysis of two mitochondrial gene fragments. Numbers on branches show ML bootstrap values (> 70). The scale bar indicates the substitution rate. The code following the species name is the specimen code.