Rapipontonia paragalene, Marin, 2007

Marin, Ivan, 2007, A new genus and species of pontoniine shrimp (Crustacea, Decapoda, Palaemonidae, Pontoniinae) associated with plumularid hydroids (Hydroidea, Plumularidae) in Vietnam, Zoosystema 29 (4), pp. 775-786 : 777-783

Rapipontonia paragalene n. sp.

( Figs 1-5 )

TYPE MATERIAL. — Holotype: Vietnam , South China Sea, Nhatrang Bay, on pile under pier of Marine Military Academy ( MMA), depth 2 m, on hydroid Lytocarpia sp., 17.VII.2006, 1 ovigerous ♀ pcl 2.5 mm (MNHN-Na 16395).

Allotype: same locality as for holotype, 1 ♂ pcl 1.8 mm (MNHN-Na 16396).

Paratypes: Vietnam , South China Sea, Nhatrang Bay, on pile under pier of MMA, depth 2 m, on hydroid Lytocarpia sp., 23.VII.2006, 4 ovigerous ♀♀ pcl 2.3, 2.6 (dissected), 3.2, 3.4 mm (photo), 1 ♂ pcl 1.7 mm ( ZMMU).

ETYMOLOGY. — The new species is closely related to Rapipontonia galene n. comb. (para, Latin for similar, resembling).

TYPE LOCALITY. — Nhatrang Bay, Vietnam .

DISTRIBUTION. — Known from the type locality, Nhatrang Bay, Vietnam .

DESCRIPTION (based on female holotype) Medium-sized shrimps with slender body ( Fig. 1 ). Carapace swollen, smooth, with well developed antennal, hepatic and epigastric teeth; hepatic tooth smaller than antennal, situated posterior and slightly above level of antennal tooth; epigastric tooth well marked, slightly smaller than proximal dorsal tooth, clearly separated from rostral teeth, separated from carapace by a well marked suture. Rostrum ( Fig. 2A, B ) long and slender, with well developed dorsal carina bearing six teeth, ventrally unarmed; proximal half of rostrum with crest-like carina bearing four large acute teeth; distal half of rostrum slender, with two small teeth. Inferior orbital angle strongly produced, rounded.

Abdominal somites smooth; tergites non-carinate, not posteriorly produced; pleura of first to fifth abdominal somites posteroventrally rounded. Telson ( Fig. 4I ) slender, four times as long as wide, tapering distally, with two pairs of small dorsal spines at 0.5 and 0.7 of telson length, respectively; posterior margin with three pairs of spines, mostlateral spines shortest, intermediate spines longest, mesial spines more slender than others, about half length of intermediate spine.

Eyes large, cornea rounded.

Antennules ( Fig. 2C ) with basal segment about three times as long as wide, with distinct ventromesial tooth; lateral portion depressed, well defined (individualized from rest of basal segment), bearing large acute distolateral tooth; stylocerite acute, reaching to about mid-length of basal segment; intermediate segment robust, about 1.5 times as long as wide; distal segment about twice as long as wide; upper (lateral) flagellum long, slender, shorter ramus with more than seven segments, with eight groups of aesthetascs; main ramus with more than 10 segments; lower (mesial) flagellum filiform, with more than 30 segments.

Antenna ( Fig. 2D ) with distolateral margin of basicerite, with distolateral tooth; carpocerite about 1.5 times as long as wide; scaphocerite slender, exceeding antennular peduncle and rostrum, about three times as long as maximum width, with well developed distolateral tooth, latter not exceeding blade.

Mouthparts without specific features. Mandible ( Fig. 3A ) without palp; incisor process slender, tapering distally, with three to four distal teeth; molar process well developed.Maxillula ( Fig. 3B ) with well developed, bilobed palp; upper lacinia larger than lower lacinia, slightly tapering distally, with strong distal spines; lower lacinia slender, distally rounded, with distal setae. Maxilla ( Fig. 3C ) with well developed, simple palp; basal endite simple, furnished with stiff, elongated setae; coxal endite absent; scaphognathite relatively broad. First maxilliped ( Fig. 3D ) with distinct endites; palp well developed, without distal setae; exopod with expanded caridean lobe bearing plumose setae marginally; epipod subtriangular. Second maxilliped ( Fig. 3E ) with normal exopod; distolateral margin of propodus broadly rounded, with slender setae; dactylus about three times as long as broad, with numerous spines along distal margin; epipod poorly developed; podobranch absent.

Third maxilliped ( Fig. 3F ) relatively slender; coxa with rounded lateral plate and several long plumose setae; basis and ischiomerus fused to single antepenultimate segment, about six times as long as wide, suture between basis and ischiomerus well marked; penultimate segment slender, about four times as long as wide; ultimate segment about four times as long as wide; exopod well developed; single arthrobranch small.

First pereiopod ( Fig. 4A ) slender, segments unarmed; basis about 1.5 times as long as wide; ischium about three times as long as wide; carpus slender, six times as long as wide; propodus about 4.5 times as long as maximum width, widening distally; palm ( Fig. 4B, C ) twice as long as wide, subcylindrical; fingers slender, about six times as long as wide, with spoon-like tips and straight cutting edges.

Second pereiopods unequal in size, symmetrical in shape ( Fig. 4D, E ); basis rectangular; ischium about five times as long as maximal width; merus about ten times as long as maximal width; carpus about three times as long as maximum width, broadening distally; palm subcylindrical ( Fig. 4E ), about three times as long as maximal width; fingers robust, about two times as long as wide, about one third of the palm length, curved, with acute tips; dactylus simple, round in cross section, without sharp cutting edge; pollex with well developed lateral carina, without sharp cutting edge ( Fig. 4F ); ratio dactylus:propodus:carpus approximately equal to 1:3:3.

Third pereiopod ( Fig. 4G ) slender; basis about twice as long as wide; ischium about four times as long as wide; merus about 10.5 times as long as wide; carpus about five times as long as maximum width, with slightly projecting distodorsal margin; propodus six times as long as wide, with broadened distal third, bearing three pairs of long spines; dactylus ( Fig. 4H ) simple, about five times longer than wide, slender, curved, forming together with long propodal spines a grasping mechanism. Fourth and fifth pereiopods similar to third.

Pleopods without specific features. Uropods ( Fig. 4J ) slender, exceeding telson; lateral margin of uropodal exopod with small subdistal tooth and adjacent spine.

Allotype male smaller in size but otherwise similar to holotype female; body somewhat more slender; endopod of first pleopod oval-shaped ( Fig. 5A ); endopod of second pleopod with well developed appendix masculina bearing two long plumose terminal setae and one simple submarginal seta ( Fig. 5B ).

Colour

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; additional broad black bands present along ventral margin of posterior abdominal segments; four narrow longitudinal black stripes on upper surface of gonads; antennules, distal uropods and telson black; distal part of propodus and fingers of second pereiopod reddish. Gonads and eggs white ( Fig. 6 ).

ECOLOGY

All specimens were found clinging onto plumulariid hydroid, Lytocarpia sp. ( Hydroidea, Thacaphora ,

Plumulariidae ) ( Fig. 6 ), growing on harbour piles, at depths of 2- 5 m.

VARIATION

In two paratype ovigerous females, largest in the type series (pcl. 3.2; 3.4 mm), the major chela is similar in proportions to the holotype, while the minor chela is comparatively more slender, with the carpus being about twice as long as the palm. Nevertheless, the proportion between the dactylus and the palm remains the same (1:3).

REMARKS

The new species is closely related to Rapipontonia galene n. comb., but can be clearly separated from the latter species by the shorter fingers and different proportions of distal segments in the second pereiopod, with the ratio dactylus:propodus:carpus of about 1:3: 3 in the holotype R. paragalene n. sp. (vs. 1:2: 4 in R. galene n. comb.; cf. Holthuis 1952: fig. 24f). In the large specimens of R. paragalene n. sp., the second pereiopods are slightly dissimilar in size, with this ratio in the minor chela being about 1: 3: 6. Rapipontonia paragalene n. sp. also differs from R. galene n. comb. by the finger tips of the first pereiopod being less distinctly scoop-shaped (vs. clearly scoop-shaped in R. galene n. comb.; cf. Bruce 1976: fig. 3d, e); and the number of distal propodal spines on the third pereiopod: three pairs of equally long spines in R. paragalene n. sp. vs. five pairs of unequal spines in R. galene n. comb. (cf. Holthuis 1952: fig. 24g), although Bruce (1976: fig. 3g) illustrated three pairs of equally long spines in R. galene n. comb. from Kenya. The colour pattern of R. paragalene n. sp. also differs from that of R. galene n. comb.; the latter species presents numerous broad black and narrow yellow longitudinal on the carapace and abdomen ( Debelius 2001: 185).

The remaining species, Rapipontonia platalea n. comb., differs from R. paragalene n. sp. by the significantly shorter, simple distal portion of the rostrum; and the second pereiopod with larger fingers, about half as long as palm (cf. Holthuis 1951: fig. 32); further, this species is distributed in the Eastern Atlantic ( Holthuis 1951; Wirtz & d’Udekem d’Acoz 2001).

Figures

FIG. 1. — Rapipontonia paragalene n.gen., n. sp.:A, female holotype from Vietnam,pcl 2.5 mm (MNHN);B, male allotype from Vietnam, pcl 1.8 mm (MNHN). Scale bar: 2 mm.

FIG. 2. — Rapipontonia paragalene n. gen., n. sp., female paratype from Vietnam, pcl 2.6 mm (ZMMU): A, anterior part of carapace, lateral view; B, same, dorsal view; C, antennule; D, antenna. Scale bars: A, B, 2 mm; C, D, 1 mm.

FIG. 3. — Rapipontonia paragalene n. gen., n. sp., female paratype from Vietnam, pcl 2.6 mm (ZMMU): A, mandible; B, maxillula; C, maxilla; D, first maxilliped; E, second maxilliped; F, third maxilliped. Scale bar: 1 mm.

FIG. 4. — Rapipontonia paragalene n. gen., n. sp., female paratype from Vietnam, pcl 2.6 mm (ZMMU): A, first pereiopod; B, C, chela of first pereiopod; D, minor second pereiopod; E, major second pereiopod; F, same, chela; G, third pereiopod; H, dactylus of third pereiopod; I, telson; J, uropod. Scale bars: A, D, E, G, I, 2 mm; B, C, H, J, 1 mm; F, 0.5 mm.

FIG. 5. — Rapipontonia paragalene n. gen., n. sp., male allotype from Vietnam, pcl 1.8 mm (MNHN): A, endopod of first pleopod; B, appendix interna and appendix masculina.

FIG. 6. — Colour pattern of Rapipontonia paragalene n. gen., n. sp., A, B, female paratype from Vietnam (ZMMU),pcl 3.4 mm,in slightly different views, on its host, the plumulariid hydroid, Lytocarpia sp. (Hydroidea, Thecaphora, Plumulariidae).