Caridina variabilirostris (Crustacea: Decapoda: Atyidae), a new species of freshwater shrimp from Pohnpei (Micronesia) Author Mazancourt, Valentin de Muséum national d’Histoire naturelle, Département Adaptations du Vivant, UMR 7208, CP 026, 57, rue Cuvier, 75231 Paris, Cedex 05, France. valentin.demazancourt@laposte.net Author Marquet, Gerard Muséum national d’Histoire naturelle, Département Adaptations du Vivant, UMR 7208, CP 026, 57, rue Cuvier, 75231 Paris, Cedex 05, France. gmarquet@neuf.fr Author Keith, Philippe Muséum national d’Histoire naturelle, Département Adaptations du Vivant, UMR 7208, CP 026, 57, rue Cuvier, 75231 Paris, Cedex 05, France. keith@mnhn.fr text European Journal of Taxonomy 2018 2018-08-03 453 1 16 journal article 22299 10.5852/ejt.2018.453 509ff7cf-3199-412b-8d01-198cb6371322 3817284 445C8252-5FA2-49AA-AB89-E1C2DDEBEE7F Caridina peninsularis Kemp, 1918 Lectotype MALAYSIA : 1 ♂ , cl 3.2 mm , Penang Island , Botanical garden , Feb. 1916 , N. Anandale leg. ( MNHN- IU-2015-1749). Paralectotypes MALAYSIA : 1 ♀ ovig., cl 5.4 mm , same data as lectotype (MNHN-IU-2015-1750); 1 ♀ , cl 3.4 mm , same data as for preceding ( NHM 1919.11.1.12-21 (1761124)); 1 ♀ ovig., cl 5.2 mm , same data as for preceding ( NHM 1919.11.1.12-21 (1761124)); 1 ♂ , cl 3.9 mm , same data as for preceding ( NHM 1919.11.1.12-21 (1761124)). Non types SINGAPORE : 1 ♀ ovig., cl 5.1 mm , Tanglin (incorrectly spelt “ Tangtum ” in NHM register and on label, see Richard & Clark 2014 ), 1958 Bedford and Lanchester leg., D.S. Johnson det. ( NHM 1958.8.7.14–17 (1749569)); 1 ♂ , cl 4.2 mm , same data as for preceding ( NHM 1958.8.7.14–17 (1749569)). Description CEPHALOTHORAX. Rostrum ( Fig. 3 a–c): very variable in length, 0.6–1.3 of cl, reaching to scaphocerite apex, armed dorsally with 18–26 teeth, distal unarmed portion 0.0–0.4 times that of armed portion, with one or two subapical teeth, 1–4 teeth on carapace posterior to orbital margin, ventral margin with 4–12 teeth. Number of dorsal teeth behind most proximal ventral tooth 12–18. Rostrum formula (1–4) 18-26+1-2/4-12. Antennular tooth acute, placed slightly below orbital angle. Pterygostomian margin rectangularly rounded. HEAD. Eyes well developed, anterior end reaching to 0.7 length of antennular peduncle basal antennomere. Antennular peduncle 0.7 times as long as carapace. Anterolateral angle reaching 0.25 length of second antennomere; second antennomere distinctly longer than third. Stylocerite reaching to 0.7 length of antennular peduncle basal antennomere. MOUTHPARTS. Mandibles dimorphic; left mandible ( Fig. 4b ) more developed, corpus large, robust with five strong sharp teeth separated by ridged gap; incisor and molar processes separated by patch of long simple setae. Right mandible ( Fig. 4c ) with five sharp incisor teeth, medially with group of long setae; molar process narrow, elongate, ridged. First maxilla ( Fig. 4d ) having a lower lacinia with margin broadly rounded, bearing several rows of plumose setae. Upper lacinia elongate, with medial margin bearing a number of distinct teeth and simple setae, palp bearing long simple setae. Second maxilla ( Fig. 4e ) upper and middle endite with marginal and submarginal simple or slightly plumose setae. Lower endite with simple setae; palp narrow, shorter than upper endite cleft with few setae. Scaphognathite fringed with long simple setae, tapering posteriorly with some long, curved simple setae at posterior end. First maxilliped ( Fig. 4h ) endopodite ultimate segment medial margin with long plumose setae. Palp elongate, setose. Exopod flagellum long and narrow distally with marginal plumose setae. Caridean lobe large, with marginal setae. Second maxilliped ( Fig. 4g ) endopodite ultimate and penultimate antennomeres fused, reflected against basal antennomeres. Ultimate, penultimate and basal antennomeres medial margins with long setae of various types ; flagellum very long, slender with marginal plumose setae distally. Third maxilliped ( Fig. 4f ) with terminal article reaching third antennular peduncle antennomere apex; distal antennomere about 10 times as long as wide, slightly shorter than penultimate, ending in large hamulate apical spine surrounded by simple setae. Penultimate antennomere about eight times as long as wide, with group of transverse rows of simple setae. Exopod flagellum well developed, about a third the length of endopodite second article, distal margin with long plumose setae. PEREOPODS. Pereopods I–IV with epipods pereopod. P1 ( Fig. 3d ): chela about 1.9–2.2 times as long as wide, movable finger 3.6–4.4 times as long as wide, 1.2–1.7 times length of palm; carpus 2.0–2.7 times as long as wide. P2 ( Fig. 3e ) more slender and longer than first pereopod with chela 2.1–2.6 times as long as wide: movable finger 3.9–5.8 times as long as wide, 1.3–2.0 times length of palm; carpus slender 4.4–6.5 times as long as wide. P3 ( Fig. 3f ): slender, dactylus ( Fig. 3g ) 2.4–3.3 times as long as wide, including terminal spine), flexor margin with 4–6 spines parallel to terminal one; propodus 13.8–20.5 times as long as wide, 4.8–8.4 times as long as dactylus. P5 ( Fig. 3h ): dactylus ( Fig. 3i ) 2.1–4.2 as long as wide with 18–29 spinules on flexor margin; propodus 15.8–28.4 times as long as wide, 5.3–8.6 times as long as dactylus. ABDOMEN. Third abdominal ( Fig. 4a ) somite with moderately convex dorsal profile. Sixth abdominal somite about 0.68 of carapace, 1.76 times as long as fifth somite, slightly shorter than telson. Telson ( Fig. 3k ) with four pairs of dorsal spines and one pair of dorsolateral spines; posterior margin, with or without median process, exhibits variations, triangular or rounded with four to five intermediate simple setae longer or equal than lateral ones. PL1 ( Fig. 3m ). Endopod foliform with a developed appendix interna in males. Pl2 ( Fig. 3n ): appendix masculina on second pleopod reaching 0.52 times length of endopod; appendix interna reaching about 0.85 times appendix masculina length. PREANAL CARINA ( Fig. 3l ). Unarmed. UROPODAL DIAERESIS ( Fig. 3j ). With 10–15 spinules. OVIGEROUS FEMALE EGG SIZE ( Fig. 3o ). 0.39–0.49x 0.24–0. 29 mm . Habitat This species is found among macrophytes in flowing fresh water of the rivers of Pohnpei all along the course, showing good adaptability to different temperatures and hydrological conditions. It is more abundant in higher elevations due to reduced predator pressure. Colour pattern ( Fig. 5 ) The colour of the body is hyaline with many reds dots. An oblique red band on the cephalothorax is very characteristic. Fig. 5. Caridina variabilirostris sp. nov. , live coloration (Photos: P. Keith) Distribution This new species is currently known from Pohnpei Island only. Remarks Caridina variabilirostris sp. nov. is most similar to C. mertoni , C. brachydactyla , C. elongapoda Liang & Yan, 1977 and C. peninsularis Kemp, 1918 . The new species displays a variable rostrum length among specimens. When the rostrum is short the general appearance is like C. mertoni , whereas when the rostrum is long, the general appearance is of C. brachydactyla . In C. variabilirostris spec. nov. the antennal spine is placed below the orbital angle, the P5 dactylus with 18–29 spinules whereas in C. mertoni , the antennal spine is somewhat fused with the orbital angle and P5 dactylus with 24–43 spinules. C. variabilirostris spec. nov. differs from C. brachydactyla by the absence of spine on the preanal carina, a shorter distal unarmed portion of the rostrum 0.0–0.4 (vs 0.4–1.6) times that of armed portion, by a longer P5 propodus, which is 5.3–8.6 time as long as the dactylus (vs 3.9–5.7) and a lower number of spinules on the P5 dactylus ( 32–42 in C. brachydactyla ). This new species resembles C. elongapoda in its preanal carina lacking a spine, but it has larger eggs 0.39–0.49 × 0.24–0. 29 mm (vs 0.39–0.40 × 0.22–0.23), and the P5 dactylus is shorter 2.1–4.2 (vs 4.3– 5.6) and with fewer spinules 18–29 (vs 33–44). It also differs from C. peninsularis by a lower number of dorsal rostrum teeth (18–26 vs 20–35), a lower P3 propodus-dactylus ratio (4.8–8.4 vs 4.4–5.8) and a P5 dactylus with 18–29 spinules vs 25–38. The new species looks very much like C. variabilis from Guam and Palau with the preanal always nonarmed, the number of teeth and their placement on the rostrum, the proportions between the joints of pereiopods, and the egg size ( Mazancourt et al. 2018 ). But the P5 dactylus has a single terminal spine and a short distal propodus seta (vs two strong distal spines and a very long distal propodus seta), and the posterior margin of the telson with intermediate setae longer or equal than lateral ones (vs shorter or equal than lateral ones).