Caridina tricincta, Do & Rintelen & Dang, 2020

Do, Van Tu, Rintelen, Thomas von & Dang, Van Dong, 2020, Descriptions of two new freshwater shrimps of the genus Caridina H. Milne Edwards, 1837 (Crustacea: Decapoda: Atyidae) from northern Vietnam, Raffles Bulletin of Zoology 68, pp. 404-420 : 407-411

Caridina tricincta , new species

( Figs. 2–4 )

Material examined. Holotype male, cl 5.3 mm ( IEBR–FS 001 ), Vietnam: Tuyen Quang Province, Na Hang District, Khau Tinh Commune , 22°26′42.1″N 105°23′09.1″E, coll. Nguyen Anh Tuan, 11 December 2014 . Paratypes: 22 females, cl 3.6–6.8 mm, 19 males, cl 4.0– 5.5 mm ( ZMB 29641), same data as holotype ; 2 males, cl 4.0 mm, 4.2 mm ( ZMB 30360), Vietnam: Ha Giang Province, Bac Me District, Lac Nong Commune , 22°44′18.635″N 105°15′37.397″E, coll. Do Van Tu & Dang Van Dong, 16 October 2019 ; 2 females, cl 3.7 mm, 4.3 mm ( ZMB 30363), Vietnam: Ha Giang Province, Bac Me District, Lac Nong Commune , 22°44′24.894″N 105°14′9.989″E, coll. Do Van Tu & Dang Van Dong, 16 October 2019 .

Comparative material. Caridina clinata Cai, Quynh & Ng, 1999 : male, cl 3.1 mm ( ZMB 30664), Vietnam: Ninh Binh Province, small stream in Cuc Phuong National Park , 20°19′11.118″N 105°37′42.168″E, coll. Thomas von Rintelen & Do Van Tu, 03 April 2017.

Description. Carapace length 3.6–6.8 mm (median 5.0 mm). Rostrum straight or slightly curved downwards, short, reaching to middle or slightly falling short of distal end of basal segment of antennular peduncle, 0.14–0.31 (median 0.25) times as long as carapace, rostral formula: 0–6+0–3/0–5 (n = 33), teeth small ( Fig. 2A ). Suborbital angle acute, completely fused with antennal spine; pterygostomian margin rounded ( Fig. 2A ). Eyes well developed with globular cornea, anterior end reaching to 0.7 times length of basal segment of antennular peduncle ( Fig. 2A ). Antennular peduncle 0.42–0.6 (median 0.49) times as long as carapace; basal segment 1.29–2.0 (median 1.71) times as long as second segment, second segment 1.14–1.5 (median 1.29) times as long as third segment ( Fig. 2B ). Stylocerite reaching distal end of basal segment of antennular peduncle ( Fig. 2B ). Scaphocerite ovate, reaching beyond distal end of antennular peduncle, 2.45–3.43 (median 2.86) times as long as wide ( Fig. 2A, C ).

Sixth abdominal somite 0.35–0.42 (median 0.4) times length of carapace, 1.47–1.91 (median 1.75) times as long as fifth abdominal somite, 0.76–0.9 (median 0.84) times length of telson. Telson length 1.91–2.75 (median 2.25) times as long as proximal wide, distal margin triangular, terminating in a very short median projection, with 4–5 pairs of dorsal spinules and one pair of dorso-subdistal spinules; distal end with 4–5 pairs of spines, lateral pair slightly longer than intermediate pairs ( Fig. 2D, E ). Preanal carina low, with few setae, lacking tooth or spine ( Fig. 2F ). Uropodal diaeresis with 12–18 movable spinules, outermost one slightly longer than lateral angle ( Fig. 2G ).

Incisor process of mandible ending in one row of 5–6 irregular teeth, molar process truncated ( Fig. 2H ). Lower lacinia of maxillula broadly rounded, upper lacinia elongated, with number of distinct teeth and setae on inner margin, palp stout with few simple setae at tip ( Fig. 2I ). Upper endites of maxilla subdivided, palp short, scaphognathite tapering posteriorly, with numerous long, curved setae at posterior margin ( Fig. 2J ). Distal end of palp of first maxilliped triangular, with a short projection; flagellum of the exopod very elongated, endopod high, reaching 0.75 times length of flagellum of exopod ( Fig. 2K, L ). Podobranch of second maxilliped incompletely reduced, with few finger-like projections ( Fig. 2M ). Third maxilliped reaching to distal end of antennular peduncle, ending in single terminal claw, exopod reaching 0.4 times length of penultimate segment; ultimate segment slightly shorter than penultimate segment ( Fig. 2N ). Branchial formula as is typical for genus, five pairs of pleurobranchs well developed; three pairs of arthrobranchs, two on third maxillipeds, with second pair strongly reduced in size, one pair on first pereopod; one pair of podobranchs on second maxilliped strongly reduced.

Epipod present on first three pereopods. First pereopod short, robust, reaching beyond end of basal segment of antennular peduncle; chela 1.69–2.14 (median 2.0) times as long as wide, 1.43–1.88 (median 1.53) times length of carpus; tips of fingers rounded, without hook; dactylus 1.08–1.67 (median 1.24) times as long as palm; carpus excavated anteriorly, 1.13–1.58 (median 1.4) times as long as wide, 0.68–0.94 (median 0.83) times length of merus; merus 2.0–2.57 (median 2.54) times as long as wide, longer than ischium ( Fig. 3A ). Second pereopod long, slender, reaching to distal end of antennular peduncle; chela 2.61–3.0 (median 2.82) times as long as wide, 0.76–0.96 (median 0.89) times length of carpus; tips of fingers rounded, without hook; dactylus 1.42–1.91 (median 1.54) times as long as palm; carpus 4.38–5.17 (median 4.71) times as long as wide, 1.0–1.13 (median 1.03) times as long as merus; merus 4.2–5.17 (median 4.85) times as long as wide, longer than ischium ( Fig. 3B ). Third pereopod slender, reaching beyond end of scaphocerite by its dactylus, terminating in two claws, with four or five accessory spines on flexor margin, dactylus 2.67–3.33 (median 2.88) times as long as wide (terminal claw and spines on flexor margin included), propodus 10.23–11.25 (median 10.86) times as long as wide, 3.8–4.8 (median 4.24) times as long as dactylus; carpus 4.15–5.18 (median 5.0) times as long as wide, 0.44–0.67 (median 0.61) times as long as propodus, 0.46–0.58 (median 0.5) times as long as merus; merus 6.12–8.68 (median 7.5) times as long as wide, bearing three strong, movable spines on posterior margin of outer surface; ischium with a small spinule ( Fig. 3C, D ). Fifth pereopod slender, reaching to end of second segment of antennular peduncle, dactylus 3.0–4.0 (median 3.25) times as long as wide (terminal claw and spines on flexor margin included), terminating in one large claw, with 33–46 spinules on flexor margin; propodus 12.0–13.0 (median 12.58) times as long as wide, 3.23–4.17 (median 3.43) times length of dactylus; carpus 4.33–5.25 (median 4.81) times as long as wide, 0.46–0.55 (median 0.5) times as long as propodus, 0.59–0.71 (median 0.64) times as long as merus; merus 6.0–7.32 (median 6.2) times as long as wide, bearing 3–4 strong, movable spines on posterior margin of outer surface ( Fig. 3E, F ).

Endopod of male first pleopod extending to 0.7 times exopod, rectangular in shape, 3.0–3.25 (median 3.0) times as long as proximal width, inner margin concave, outer margin slightly convex, rounded distally, long plumose setae on outer and distal margins, medium-length setae on inner margin; with appendix interna exceeding terminal margin of endopod by 0.3–0.5 its length ( Fig. 3G, H ). Appendix masculina of male second pleopod stout, reaching to proximal 0.5 times endopod length, 6.0 times as long as distal width, fingershaped, with some short spinules on outer surface and some long spinules on distal surface; appendix interna at the middle of appendix masculina, extending about 0.9 times length of appendix masculina ( Fig. 3I, J ).

Habitat. This species was found in a stream with mixed sand, gravel, and rock substratum, and clear flowing water from the forest ( Fig. 4A ).

Colouration. The body is dark grey. Three black transverse stripes are present on the carapace, third and sixth abdominal somites, respectively, interleaved with three narrower grey transverse stripes ( Fig. 4 ).

Etymology. The name ‘ tricincta ’ (L. tri – three; cinctus – belt or girdle) refers to the three characteristic transverse stripes on the body of live specimens of this species. Used as an adjective.

Remarks. Caridina tricincta , new species, is quite similar to C. clinata Cai, Quynh & Ng, 1999 , from Ninh Binh province, northeast Vietnam, in the shape of the endopod of male first pleopod. However, it can be separated by the number of teeth located on the dorsal surface including the teeth on the carapace posterior to the orbital margin (0–7 teeth vs. 13–21 teeth); proportion of the chela of the second pereopod (2.61–3.0 times as long as wide vs. 2.5 times as long as wide); proportion of the propodus of the third pereopod (10.23–11.25 times as long as wide vs. 9 times as long as wide in C. clinata ; and 3.8–4.8 times as long as dactylus vs. 3.6 times as long as dactylus in C. clinata ); proportion of the endopod of the male first pleopod (3.0–3.25 times as long as wide vs. 2.8 times as long as wide in C. clinata ); and the live colour patterns (distinct and unbroken black transverse stripes are present vs. black patterns are unobvious, thin and irregularly broken in C. clinata ) ( Figs. 2A , 3B, H , 4A, B ; cf. Cai et al., 1999: figs. 1A–C, G–I, 2F).

Caridina tricincta , new species, is also similar to C. baoting Cai, 2014 , from Hainan Island and C. serrata Stimpson, 1860 , from Hong Kong, southern China, in the shape of the rostrum and the endopod of male first pleopod. Caridina tricincta , new species, can be distinguished from C. baoting by a suite of characteristics: the fingers of the first pereopod are slightly longer than the palm (vs. as long as palm in C. baoting ); the carpus of the first pereopod is 1.13–1.58 times as long as wide (vs. 1.7 times as long as wide in C. baoting ); the chela of the second pereopod is 2.61–3.0 times as long as wide (vs. 2.4 times as long as wide in C. baoting ); the endopod of male first pleopod is 3.0–3.25 times as long as wide (vs. 2.8 times as long as wide in C. baoting ); the appendix interna extends about 0.9 times length of appendix masculina (vs. 0.4 times length of appendix masculina in C. baoting ); and the uropodal diaeresis has 12–18 movable spinules (vs. 20–23 movable spinules in C. baoting ) ( Figs. 2 , 3 ; cf. Cai, 2014: figs. 8, 9).

When compared to C. serrata Stimpson, 1860 , the new species Caridina tricincta can be easily distinguished, by fewer teeth on the dorsal margin of the rostrum (excluding the teeth on the carapace posterior to orbital margin) (viz. 0–3 teeth vs. 5–12 teeth in C. serrata ), and a shorter stylocerite, just reaching the distal end of basal segment of the antennular peduncle (vs. extending beyond the end of basal segment of the antennular peduncle in C. serrata ) ( Fig. 2A, B ; cf. Cai & Ng, 1999: figs. 2, 3).

The rostrum shape and the endopod of male first pleopod of Caridina tricincta , new species, are quite similar to that of C. sumatianica Cai & Yuan, 1996 , from Hongyan Village, Chishui region, Guizhou Province, China. However, C. tricincta , new species, can be distinguished from C. sumatianica by the number and position of the ventral teeth of the rostrum (0–5 not close to the tip vs. 2–4 teeth close to tip in C. sumatianica ); the stylocerite reaching the end of the basal segment of the antennular peduncle (vs. stylocerite only 0.75 times length of basal segment in C. sumatianica ); and the endopod of the male first pleopod being 3.0–3.25 times as long as its proximal width (vs. 2.5 times in C. sumatianica ) ( Figs. 2A, B , 3H ; cf. Cai & Yuan, 1996: figs. 22, 23).

Figures

Fig. 2. Caridina tricincta, new species. A, holotype male, cl 5.3 mm (IEBR–FS 001); B–N, paratype male, cl 4.3 mm (ZMB 29641). 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: A–C, F = 1 mm; E, G–N = 0.5 mm.

Fig. 3. Caridina tricincta, new species. Paratypes male, cl 4.3 mm (ZMB 29641). A, first pereopod; B, second pereopod; C, third pereopod; D, the same, dactylus; E, fifth pereopod; 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: A–J = 0.5 mm.

Fig. 4. Caridina tricincta, new species. A, in situ photograph (by Nguyen Anh Tuan) at a stream of Khau Tinh Commune, Na Hang District, Tuyen Quang Province; B, live individuals collected in Lac Nong Commune, Bac Me District, Ha Giang Province.