Caridina pacbo, 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 : 411-414

Caridina pacbo , new species

( Figs. 5–7 )

Material examined. Holotype male, cl 4.2 mm ( IEBR–FS 003 ), Vietnam: Cao Bang Province, Ha Quang District, Truong Ha Commune, Pac Bo Village , small stream in Khuoi Nam , 22°59′1.7″N 106°02′31.2″N, coll. Do Van Tu, 25 May 2017 . Paratypes: 5 females, cl 5.0– 6.3 mm; 2 males, cl 4.2–4.5 mm ( ZMB 30295), same data as holotype .

Comparative material. Caridina nguyeni Li & Liang, 2002 : male, cl 3.2 mm ( ZMB 30280), Vietnam: Cao Bang, Ha Quang, Truong Ha, Pac Bo , a small creek run into Le Nin stream, 22°59′4.0″N 106°02′53.7″E, coll. Do Van Tu, 25 May 2017; male, cl 3.3 mm ( ZMB 30283), Vietnam: Cao Bang, Ha Quang, Lung Nam, a small stream runs along the road of Thin Tang village , 22°58′33.99″N 106°04′7.06″E, coll. Do Van Tu, 25 May 2017 . Caridina cucphuongensis Dang in Dang, Thai & Pham, 1980: male, cl 3.8 mm; 2 females, cl 4.2–4.4 mm ( ZMB 30234), Vietnam: Ninh Binh, Cuc Phuong National Park , a small stream near the footpath to the one thousand year old tree (in Vietnamese name: chò), 20°21′0.779″N 105°36′11.675″E, coll. Thomas von Rintelen & Do Van Tu, 03 April 2017 .

Description. Carapace length 4.2–6.3 mm (median 5.2 mm). Rostrum slightly curved downwards, short, reaching beyond middle or close to end of basal segment of antennular peduncle, 0.25–0.36 (median 0.3) times as long as carapace, rostral formula: 5–12+2–6/0–3 (n = 8), teeth small ( Fig. 5A ). Suborbital angle acute, completely fused with antennal spine; pterygostomian margin rounded ( Fig. 5A ). Eyes well developed with globular cornea, anterior end reaching to 0.6 times length of basal segment of antennular peduncle ( Fig. 5A ). Antennular peduncle 0.35–0.62 (median 0.49) times as long as carapace; basal segment 1.38–1.67 (median 1.67) times as long as second segment, second segment 1.2–1.33 (median 1.33) times as long as third segment ( Fig. 5B ). Stylocerite mostly reaching beyond the end of basal segment, sometimes to the middle of second segment of antennular peduncle ( Fig. 5B ). Scaphocerite ovate, reaching beyond distal end of antennular peduncle, 2.64–3.13 (median 2.73) times as long as wide ( Fig. 5C ).

Sixth abdominal somite 0.37–0.51 (median 0.46) times length of carapace, 1.25–1.77 (median 1.4) times as long as fifth somite, 0.95–1.08 (median 1.0) times length of telson. Telson length 1.77–1.92 (median 1.91) times as long as proximal wide, distal margin round with median projection, with 4–5 pairs of dorsal spinules and one pair of dorso-subdistal spinules; distal end with four pairs of spines, lateral pair slightly longer than intermediate pairs ( Fig. 5D, E ). Preanal carina high, with few setae, lacking a spine ( Fig. 5F ). Uropodal diaeresis with 19–20 movable spinules, outermost one as long as lateral angle ( Fig. 5G ).

Incisor process of mandible ending in one row of six irregular teeth, molar process truncated ( Fig. 5H ). Lower lacinia of maxillula broadly rounded, upper lacinia elongated, with a number of distinct teeth and setae on inner margin, palp short and stout with few simple setae at tip ( Fig. 5I ). Upper endites of maxilla subdivided, palp short, scaphognathite tapering posteriorly, with numerous long, curved setae at posterior margin ( Fig. 5J ). Distal end of palp of first maxilliped triangular, with a short projection; flagellum of the exopod very elongated, endopod high, reaching 0.67 times length of the flagellum of exopod ( Fig. 5K, L ). Podobranch of second maxilliped incompletely reduce to a lamina with few fingerlike projections ( Fig. 5M ). Third maxilliped reaching to end of antennular peduncle, ending in single terminal claw, exopod reaching to 0.3 times length of penultimate segment; ultimate segment as long as penultimate segment ( Fig. 5N ). 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 four pereopods. First pereopod short, robust, reaching the end of basal segment of antennular peduncle; chela 2.07–2.40 (median 2.2) times as long as wide, 1.45–1.6 (median 1.5) times length of carpus; tips of fingers rounded, without hook; dactylus 0.75–0.95 (median 0.83) times as long as palm; carpus excavated anteriorly, 1.31–1.67 (median 1.5) times as long as wide, 0.75–0.88 (median 0.8) times length of merus; merus 2.75–3.8 (median 2.78) times as long as wide, 1.21–1.29 (median 1.25) times longer than chela, longer than ischium ( Fig. 6A ). Second pereopod long, slender, reaching to end of antennular peduncle; chela 2.67–3.09 (median 2.82) times as long as wide, 0.77–0.86 (median 0.78) times length of carpus; tips of fingers rounded, without hook; dactylus 1.57–1.78 (median 1.67) times as long as palm; carpus 4.25–5.0 (median 4.89) times as long as wide, as long as merus; merus 5.0–5.86 (median 5.45) times as long as wide, longer than ischium ( Fig. 6B ). Third pereopod slender, reaching beyond end of scaphocerite by its dactylus, terminating in one claw, with four or five accessory spines on flexor margin, dactylus 2.25–2.5 (median 2.47) times as long as wide (terminal claw and spines on flexor margin included), propodus 8.4–9.33 (median 8.98) times as long as wide, 3.89–4.2 (median 4.19) times as long as dactylus; carpus 4.71–5.54 (median 4.88) times as long as wide, 0.76–0.83 (median 0.78) times as long as propodus, 0.51–0.58 (median 0.54) times as long as merus; merus 5.56–6.36 (median 6.05) times as long as wide, bearing three strong, movable spines on posterior margin of outer surface; ischium with a small spinule ( Fig. 6C, D ). Fifth pereopod slender, reaching to end of second segment of antennular peduncle, dactylus 2.25–2.5 (median 2.47) times as long as wide (terminal claw and spines on flexor margin included), terminating in one large claw, with 28–45 spinules on flexor margin; propodus 11.78–12.57 (median 12.13) times as long as wide, 4.89–5.3 (median 4.90) times length of dactylus; carpus 4.0–4.6 (median 4.15) times as long as wide, 0.5–0.57 (median 0.54) times as long as propodus, 0.63–0.66 (median 0.64) times as long as merus; merus 5.06–5.47 (median 5.13) times as long as wide, bearing 3–4 strong, movable spines on posterior margin of outer surface ( Fig. 6E, F ).

Endopod of male first pleopod extending to 0.8 times exopod, rectangular in shape, anterior region folding backwards, 2.86–3.33 (median 3.09) 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 distinctly exceeding terminal margin of endopod ( Fig. 6G, H ). Appendix masculina of male second pleopod slender, reaching to proximal 0.7 times endopod length, 8.0 times as long as distal width, rod-shaped, with some short spinules on outer surface and some long spinules on distal surface; appendix interna at the middle of appendix masculina, extending about 0.6 times length of appendix masculina ( Fig. 6I, J ).

Habitat. This new species was found in a streamlet with mixed sand, gravel, and bedrock substratum, and clear flowing water from the forest ( Fig. 7 ).

Figures

Fig. 5. Caridina pacbo, new species. A, holotype male, cl 4.2 mm (IEBR–FS 003); B–N, paratypes male, cl 4.3 mm (ZMB 30295). 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. 6. Caridina pacbo, new species. Paratypes male, cl 4.3 mm (ZMB 30295). 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. 7. Habitat of Caridina pacbo, new species, in Pac Bo village, Truong Ha Commune, Ha Quang District, Cao Bang Province.