Rapipontonia hydra, Marin, Ivan, 2009

Marin, Ivan, 2009, A review of the pontoniine shrimp genus Rapipontonia Marin, 2007 (Decapoda: Caridea: Palaemonidae), with the description of a new species from the Indo-West Pacific, Zootaxa 2289, pp. 1-17 : 10-14

Rapipontonia hydra n. sp.

( Figs. 5–7 )

Rapipontonia paragalene . — Marin, 2007: 777 [partim], figs. 2, 3, 6.

Material. 1 ovigerous female, pcl 3.4 mm (holotype, MNHN-Na17186), 1 ovigerous female, pcl. 3.2 mm ( ZMMU), Pacific Ocean, Vietnam, Nhatrang Bay, on pile under pier of MMA, depth 2 m, on hydroid Lytocarpia sp., 23 July 2006; 1 non-ovigerous female, pcl. 1.6 mm ( ZMMU), Nhatrang Bay, N of Nha Trang, off Hon Chong Beach, 12°16' 21.4" N; 109°12' 13.5" E, depth 1.5 m, 12 Aug. 2008, coll. Z. Duris & I. Horka; 4 females, 8 males ( RMNH D 48164), Pacific Ocean, Indonesia, Moluccas, Ambon, Leitimur, Ambon Bay, outer bay, Tg. Benteng (= Galghoek); STA RBE 0 5, 0 9 Nov. 1990; depth 2–4 m, on hydroids; coll. Fransen & Lavaleye.

Description. Medium-sized shrimp with body slender. Carapace ( Fig. 5 A–C) smooth, well developed antennal and hepatic teeth; hepatic tooth larger situated above and posterior to antennal; with small epigastric tooth divided from carapace by a suture, clearly separated from posterior dorsal rostral tooth. Rostrum ( Fig. 5 A, C) long, slender and straight, overreaching distal margin of antennular peduncle ( Fig. 5 C), with well developed dorsal crest bearing 4–5 teeth; with distal part produced and very slender with one medium and small subapical teeth; ventral margin unarmed, proximally setose. Inferior orbital angle bluntly produced.

Abdominal segments smooth, tergites non-carinate or posteriorly produced; pleura of first to fifth abdominal segments rounded posteroventrally. Telson ( Fig. 5 D) slender, about 3 times as long as wide, tapering distally, with two pairs of small dorsal spines at 0.5 and 0.75 of the length, with three pairs of posterior marginal spines.

Eyes ( Fig. 5 B) large, with cornea rounded. Eyestalk about twice longer than wide, with the diameter similar to cornea.

Antennule ( Fig. 5 E) well developed; basal segment about 3 times as long as wide; stylocerite acute, triangular, reaching almost to middlelenght of basal segment; dorso medial part of the segment bearing a row of long plumose setae; disto-lateral margin with slender and acute distolateral tooth and accompanying bluntly produced triangular lobe; ventral tooth small situated at the middle-length of the segment. Intermediate antennular segment slender, about twice longer than wide, with a series of long plumose setae along outer lateral margin. Distal antennular segment shorter than intermediate, about as long as wide. Upper flagellum biramous, fused part consisting of 5–7 segments, shorter free ramus with 5–6 segments, with 10 groups of aesthetascs, longer free ramus and lower flagellum slender, filiform.

Antenna ( Fig. 5 F) well developed, basicerite with acute distolateral tooth; carpocerite about twice longer as wide, not reaching middle of scaphocerite; flagellum well developed; blade of scaphocerite slightly exceeding antennular peduncle and not overreaching rostrum, about 4 times as long as maximum width, with distolateral tooth slender and acute, not exceeding lamina.

Mouthparts are typical for the genus. Third maxilliped ( Fig. 5 G) with two long plumose setae on coxal segment, with ear-shaped epipod and small arthrobranch.

First pereiopod ( Fig. 6 A) slender, with unarmed segments; merus about 8 times longer than wide; carpus about 6 times longer than wide, flaring distally; chela ( Fig. 6 B) subcylindrical, about 2.5 times longer than wide; fingers equal to palm length, straight, simple, with spoon-shaped tips.

Second pereiopods smooth, with unarmed segments, long and slender, unequal in size in females and equal in males. In females, major second pereiopod ( Fig. 6 C) long and slender, with distal margin of carpus overreaching distal margin of antennular peduncle; merus about 10 times longer than wide, carpus about 7 times longer than maximal width, flaring distally, palm ( Fig. 6 D) about 6 times longer than wide, ratio of merus: carpus: propodus: dactylus is 6.5: 5: 4.5: 1; minor second pereiopod ( Fig. 6 E) with merus about 10 times longer than wide, carpus about 9 times longer than maximal width, flaring distally, palm ( Fig. 6 F) about 4.5 times longer than wide, ratio of merus: carpus: propodus: dactylus is 5.5: 5: 2.5: 1. In males, second pereiopods ( Fig. 7 E, G) equal in size and shape, reaching to the distal margin of antennular peduncle, slender, with merus about 11 times longer than wide, carpus about 7 times longer than maximal width, flaring distally, palm ( Fig. 7 F, H) about 3.5 times longer than wide, ratio of merus: carpus: propodus: dactylus is 3.5: 3: 2: 1.

Third pereiopod ( Fig. 6 G) slender, not exceeding scaphocerite, segment smooth, unarmed; merus about 13 times longer than wide, about 1.5 longer than carpus; carpus about 8 times longer than maximal width, flaring distally; propodus about 9 times longer than wide, about 1.2 times longer than carpus, with 2–3 unpaired long spines situated in distal third of ventral margin, pair of long distoventral spines situated to the distoventral margin proximally by 1/10 of the length of the segment ( Fig. 6 H); dactylus, simple, long and curved. Fourth and fifth pereiopods generally similar to third.

Pleopods normal. Uropods ( Fig 5 D) slender, exceeding telson; lateral border of uropodal endopod straight, with small distolateral tooth and slender mobile spine.

Endopod of second male pleopod with well developed appendices; appendix masculina ( Fig. 5 H) with one apical long plumose setae and three long simple setae situated along lateral margin.

Remarks. The new species can be distinguished from the most similar R. paragalene by: 1) longer rostrum with the most distal tooth on the dorsal crest reaching the distal margin of the basal antennular segment, the subapical dorsal tooth overreaching the antennular peduncle; 2) carpus of the minor second pereiopod longer, about twice the palm length; 3) third pereiopod usually with three long unpaired spines with the most proximal one similar to the length of the previous spine (vs. usually only two unpaired spines in R. paragalene ; if the third proximal spine presents, it not exceed the half of the length of the previous one). Besides, the new species is the largest known species within the genus.

Coloration. Body, appendages and eyestalks translucent, with numerous large white chromatophores ordered in longitudinal bands along carapace and abdomen; first to fourth abdominal pleurae with oblique black bands; black thin band crossing the ventral surface of the body from flagella and outer margin of antenna to the distal margin of telson; four narrow longitudinal black stripes on upper surface of gonads; distal part of propodus and fingers of second pereiopod reddish. Gonads and eggs white (see Marin, 2007: Fig. 6 ). The species coloration is similar to coloration of R. paragalene but the latter species is more transparent with less densely set white chromatophores on the body, concentrated mainly on the dorsal surface of the body.

Etymology. The name of the new species is given according to it hosts, hydroids (Hydroidea).

Hosts and distribution. The species is known from Vietnam (type locality) and Indonesia. The specimens were found in association with plumulariid hydroid Lytocarpia sp. (Cnidaria, Hydroidea, Plumulariidae ).

Figures

FIGURE 5. Rapipontonia hydra n. sp.., paratypes, female (A, C, D, E-G), male (B, H) (RMNH, D 48164): A, Bcarapace and rostrum, lateral view; C—same, dorsal view; D—telson and uropods; E—antennula; F—antenna; G—third maxilliped; H—appendix masculine. Scale bar: 1 mm.

FIGURE 6. Rapipontonia hydra n. sp., paratype female, (RMNH, D 48164): A—first pereiopod; B—same, chela; Cmajor second pereiopod; D—same, chela; E—minor second pereiopod; F—same, chela; G—third pereiopod; H—same, grasping mechanism. Scale bar: 1 mm.

FIGURE 7. Sexual dimorphism in morphology of second pereiopods in Rapipontonia hydra n. sp., paratypes, female (A – D), male (E – H) (RMNH, D 48164): A—major second pereiopod of female; B—same, chela; C—minor second pereiopod of female; D—same, chela; E, G—second pereiopods of male; F, H—same, chela. Scale bar: 1 mm.