Caridina danxiaensis, Wang & Chu & Ma, 2024

Wang, Yaqin, Chu, Ka Hou & Ma, Ka Yan, 2024, Description of a new species of freshwater shrimp (Decapoda: Caridea: Atyidae) from Mount Danxia, Guangdong, China, based on morphological and molecular evidence, Zootaxa 5476 (1), pp. 447-462 : 448-460

Caridina danxiaensis sp. nov.

( Figs. 1–3 )

Type material. Holotype: male (cl 4.2 mm, tbl 14.5 mm) (SYS_Csp_GDDXWLG3_13), collected by hand nets, Wolong Hill , Danxia Mountain National Nature Reserve of Shaoguan City , Renhua County, Shaoguan City, Guangdong province, China, 113°45’21.02”E, 25°0’12.48”N, 02 April 2022 . Paratypes: 3 females (cl 4.3mm, tbl 14.5 mm; cl 4.8 mm, tbl 15.4 mm; cl 4.2mm, tbl 14.2 mm) (SYS_Csp_GDDXWLG3_7, SYS_Csp_GDDXWLG3_ 8, SYS_Csp_GDDXWLG3_14), same collection data as holotype .

Description. Carapace ( Fig. 1A ) length 4.2–4.8 mm. Rostrum short, straight, rather slender, dorsal margin nearly horizontal, reaching to midlength of second segment of antennular peduncle, 0.55–0.58 times as long as carapace; rostral formula 5–8+7–8/0 evenly spaced teeth. Suborbital angle indistinct, partially fused with antennal spine, pterygostomian margin rounded.

Eyes well developed, anterior end reaching to 0.61–0.64 times length of basal segment of antennular peduncle. Antennular peduncle 0.50–0.51 times as long as carapace, basal segment of antennular peduncle longer than sum of second and third segment length, anterolateral angle pointed, reaching 0.25 times length of the second segment, second segment distinctly longer than third segment ( Fig. 1B ). Stylocerite reaching distal end of basal segment of antennular peduncle. Scaphocerite ovate, 3.8–3.9 times as long as wide, lateral tooth not nearly reaching distal margin of scaphocerite ( Fig. 1C ).

Sixth abdominal somite 0.46–0.48 times length of carapace, 1.33–1.47 times as long as fifth somite, slightly shorter than telson. Telson 4.5–4.8 times as long as proximal wide, distal margin triangular, terminating in a short median projection, with 4 pairs of dorsal spiniform spines and one pair of dorso-subdistal spiniform setae; posterior margin with 4 pairs of nearly equal long intermedial plumose setae ( Fig. 1D ). Preanal carina unarmed. Uropodal diaeresis with 19–23 movable spiniform setae ( Fig. 1E ).

Mandible ( Fig. 1F ) without palp; left incisor process with 6 sharp teeth; medially with two groups of setae; molar process ridged.

Maxillula ( Fig. 1G ) with simple and stout palp, bearing few simple setae at tip; lower lacinia broadly rounded, upper lacinia broadly elongated, inner edge straight, with distinct teeth and setae.

Maxilla ( Fig. 1H ) with scaphognathite tapers posteriorly, with numerous long plumose setae at posterior margin distally and short marginal setae continuing down proximal triangular process; upper and middle endites with marginal simple, and sub-marginal simple setae.

First maxilliped ( Fig. 1I ) with palp broadly triangular ending in finger-like tip and with terminal long plumose setae; caridean lobe broad; exopodal flagellum well developed; distal end of endopod with numerous long setae.

Second maxilliped ( Fig. 1J ) with inner margin of ultimate and basal segments with dense long setae, penultimate segments with 11 long plumose setae; exopod long with long plumose setae; podobranch well developed, with finger-like projections.

Third maxilliped ( Fig. 2A ) nearly reaches to distal end of second antennular peduncle segment, endopod threesegmented, ending in single terminal claw, ultimate segment slightly shorter than penultimate segment; exopod reaching 0.36 times length of penultimate segment; serrate setae; exopod reaches to 0.45–0.50 times of second segment of endopod, distal margin with long plumose setae. Branchial formula typical for genus.

First pereiopod ( Fig. 2B ) chela 2.0–2.2 times as long as wide, 1.50–1.70 times as long as carpus; dactylus 0.89–1.02 times as long as palm; carpus strongly excavated distally, 1.27–1.46 times as long as wide, 0.63–0.77 times as long as merus.

Second pereiopod ( Fig. 2C ) chela 2.72–2.78 times as long as wide, 0.78–0.88 times as long as carpus; dactylus 1.6–2.0 times as long as palm; carpus 4.2–4.4 times as long as wide, 1.10–1.14 times as long as merus.

Third pereiopod ( Fig. 2D ) not sexually dimorphic, dactylus with 5 accessory spiniform setae on flexor margin, 2.9–3.2 times as long as wide (terminal claw and accessory spiniform setae included); propodus 8–9 times as long as wide, 3.9–4.1 times as long as dactylus, bearing 12–14 strong, movable spiniform setae on posterior margin of outer surface; carpus bearing two movable spiniform setae on posterior margin of outer surface; ischium without movable spiniform seta.

Fourth pereiopod extending to distal end of second segment of antennular peduncle; its structure and form similar to third pereiopod.

Fifth pereiopod ( Fig. 2E, F ) dactylus with 26–32 accessory spiniform setae on flexor margin, terminating in one large claw, 1.85–2.09 times as long as wide (terminal claw and accessory spiniform setae included); propodus 8.2–9.5 times as long as wide, 4.6–5.0 times as long as dactylus, bearing 8–10 strong, movable spiniform setae on posterior margin of outer surface; carpus bearing one movable spiniform setae on posterior margin of outer surface; ischium without movable spiniform seta.

Epipods present on first four pereiopods.

Endopod ( Fig. 2G ) of male first pleopod subrectangular, anterior part not folded backward, 3.79 times as long as wide, about 0.74 times as long as exopod, inner margin concave, outer margin slightly convex, rounded distally, long plumose setae on outer and distal margins, strong and short setae on inner margin; with appendix interna exceeding terminal margin of endopod by 0.37 its length.

Appendix masculina of second pleopod ( Fig. 2H, I ) rod-shaped, 7.51 times as long as distal width, reaching to about 0.65 times length of endopod, with some short spiniform setae on basal part and some long spiniform setae on outer and distal surface; appendix interna at the middle of appendix masculina, extending about 0.8 times length of appendix masculine, distally with many cincinulli.

Coloration. Body semi-translucent, light grey with red dots on the carapace ( Fig. 3B ).

Habitat. This species was found in a stream with mixed sand, mud, gravel, and rock substratum, and clear flowing water from the forest ( Fig. 3A ).

Molecular results. The aligned 16S rRNA sequence dataset consisted of 541bp. The 16S rRNA sequences of the four individuals of Caridina danxiaensis sp. nov. from Danxia Mountain National Nature Reserve were identical. The interspecific pairwise genetic distances between Caridina danxiaensis (n = 4) and 28 morphologically/ genetically similar or closely distributed Caridina species varied from 0.057 ( Caridina clinata ) to 0.13 ( Caridina lanceifrons ) ( Table 1 ), clearly supporting C. danxiaensis sp. nov. as a distinct taxon.

Etymology. The new species is named after Danxia Mountain National Nature Reserve located in Renhua County, Guangdong Province, China. The name Danxia also refers to various landforms found in southeast, southwest, and northwest China and consisting of a red bed with steep cliffs. This is a unique type of petrographic geomorphology.

Chinese name: 丹AEẊợ (dân xiá mǐ xiâ), meaning Danxia shrimp.

Remarks. Caridina danxiaensis sp. nov. shows some morphological similarities to C. baoting Cai, 2014 , C. caobangensis Li & Liang, 2002 , C. clinata Cai, X.Q. Nguyên & Ng, 1999 , C. conghuensis Klotz & von Rintelen, 2014 , C. cucphuongensis Dang, 1980 , C. haivanensis Do & Dang, 2010 , C. macauensis Zhou, Zhang, Wong & Huang, 2021 , C. pacbo Do, von Rintelen & Dang, 2020 , C. pingi Yü, 1938 , C. pseudoserrata, Dang & Do, 2007 , C. rubropunctata Dang & Do, 2007 , C. serrata Stimpson, 1860 , C. songtaoensis Liang, 2004 , C. tetrazona Chen, Chen, Zheng & Guo, 2020 , and C. tricincta Do, von Rintelen & Dang, 2020 by possessing a short rostrum. However, the remarkable feature of the short and slender, dorsally armed but ventrally unarmed rostrum of the new species is unusual for the genus Caridina . Caridina danxiaensis sp. nov. can be easily distinguished from these species by the characters shown in Table 2 . Cardina cuphuongensis , C. pacbo and C. serrata sometimes also lack ventral rostral teeth and there are overlaps in the rostrum formula and number of spiniform setae at the uropodal diaresis in these species with the new species. However, the stylocerite of C. danxiaensis sp. nov. merely reaches beyond distal end of basal segment of antennular peduncle, never reaching the middle of second segment of antennular peduncle, while that of C. cuphuongensis is much longer than the new species, reaching to the distal end of second segment of antennular peduncle or at least 0.7 times of it. Caridina pacbo and C. serrata bear a short rostrum never reaching to midlength of second segment of antennular peduncle, while that of Caridina danxiaensis sp. nov. reaching to midlength of second segment of antennular peduncle.

According to the 16SrRNA sequence analyses, Caridina danxiaensis sp. nov. is closely related to C. clinata , C. rubropunctata , and C. trifasciata . Morphologically, C. clinata , and C. danxiaensis sp. nov. share a short rostrum, but the uropodal diaeresis of C. clinata bears much fewer (14–17) movable spiniform setae. The length of the stylocerite of C. rubropunctata and C. trifasciata is similar to the new species. However, the ventral margin of C. rubropunctata and C. trifasciata is armed with teeth. Overall, C. danxiaensis sp. nov. differs morphologically from the three species and other congeners by a relatively short rostrum just reaching to the midlength of the second segment of the antennular peduncle with rostral formula of 5–8+7–8/0, stylocerite reaching end of basal segment of antennular peduncle, and uropodal diaeresis with 19–23 movable spiniform setae.

Figures

FIGURE 1. Caridina danxiaensis sp. nov.: A, C–E from holotype male, (SYS_Csp_GDDXWLG3_13); B, F–J from paratype female (SYS_Csp_GDDXWLG3_7).A, cephalothorax and cephalic appendages, lateral view; B, left antennule, lateral view; C, right antenna with scaphocerite, lateral view; D, telson, dorsal view; E, right uropodal diaeresis, lateral view; F, mandible, lateral view; G, maxillula, lateral view; H, maxilla, lateral view; I, first maxilliped, lateral view; J, second maxilliped, lateral view.

FIGURE 2. Caridina danxiaensis sp. nov.: A–C from holotype male, (SYS_Csp_GDDXWLG3_13); D–I from paratype female (SYS_Csp_GDDXWLG3_8). A, right third maxilliped, lateral view; B, right first pereiopod, lateral view; C, right second pereiopod, lateral view; D, right third pereiopod, lateral view; E, right fifth pereiopod, lateral view; F, dactylus of fifth pereiopod, lateral view. G, endopod of first right pleopod, lateral view; H, I, appendix masculina of second right pleopod, lateral view.

FIGURE 3. A, collection site of Caridina danxiaensis sp. nov. in Shaoguan Danxia Mountain National Nature Reserve; B, photos of live specimens of Caridina danxiaensis sp. nov.