A new species of the pontoniine shrimp genus Eupontonia (Crustacea: Decapoda: Caridea: Palaemonidae) from the Ryukyu Islands, Japan Author Komai, Tomoyuki Author Minemizu, Ryo text Zootaxa 2014 3784 2 171 178 journal article 46116 10.11646/zootaxa.3784.2.6 a920b177-3f94-4ff5-b384-e46e5092ca87 1175-5326 224484 CC68C27D-D614-41AF-A8A6-27BDE6D5CECF Eupontonia gracilipes n. sp. [New Japanese name: Awamori-kakure-ebi] Figs. 1–4 Material examined. Holotype : off Osaki, Ishigaki Island, Yaeyama Islands, Ryukyu Islands, 5 m , under coral rubble, 4 November 2011 , coll. R. Minemizu, SCUBA diving, female (cl 3.2 mm ), CBM-ZC 12300. Description. Body ( Fig. 1 A, D) subcylindrical; tegmental surface glabrous. Rostrum ( Fig. 1 A, B) moderately slender, straight, about 0.4 of carapace length, directed forward, nearly reaching distal margin of second segment of antennular peduncle; dorsal margin armed with 6 teeth, including 1 posterior to rostral base located at 0.1 of carapace length; ventral margin slightly convex in lateral view, with 2 small teeth in distal 0.4; lateral surface with sharp carina in proximal half, merging into orbital margin. Carapace ( Fig. 1 A, B) with low but distinct postrostral median ridge extending to midlength; postorbital ridge distinct, delimiting deep orbital concavity; suborbital angle not produced; antennal tooth moderately small, directed forward; pterygostomial angle slightly produced, rounded. Epistome with pair of low protuberances on either side of midline. Labrum large, well produced, seen in lateral view ( Fig. 1 A). Fourth thoracic sternite ( Fig. 1 C) with spine-like median process directed anteroventrally and pair of small teeth laterally on anterior margin. Fifth sternite ( Fig. 1 C) with pair of acute submedian teeth separated by U-shaped notch. Posterior sternites unarmed. Pleon ( Fig. 1 D) dorsally rounded. First to fourth pleura rounded, fifth and sixth pleura each with small posteroventral tooth. Sixth pleomere 1.6 times as long as fifth pleomere and 1.4 times longer than high; posterolateral process terminating in sharp tooth. Telson ( Fig. 1 D, E) about 1.3 times as long as sixth pleomere and 2.4 times as long as wide, armed with 1 left and 2 right long dorsolateral spines (anterior spine located at 0.3 of telson length, posterior pair at about midlength); lateral margin parallel in anterior half, tapering to convex posterior margin in posterior half; posterior margin armed with 3 pairs of spines, lateral pair moderately short, intermediate pair elongate, about 0.3 times as long as telson, mesial pair slender, about 0.6 length of intermediate pair. Eye ( Fig. 1 A, B) with cornea fairly reduced in size, semispherical, darkly pigmented, much shorter and narrower than eyestalk; no ocellar spot evident. Eyestalk somewhat inflated with lateral and mesial faces convex. Antennular peduncle ( Fig. 1 A, B) reaching distal 0.3 of antennal scale. First segment broad, lateral margin slightly convex, distolateral angle produced, terminating in small sharp tooth; dorsal surface concave; ventromesial margin with small acute tooth at about midlength; stylocerite short, acute, located proximal to midlength of first peduncular segment. Second segment less than 0.3 length of first segment. Third segment slightly longer and narrower than second segment. Lateral flagellum biramous, 10 proximal articles fused; shorter ramus ( Fig. 1 F) very short, consisting of 5 articles, distal 4 article each bearing 1 or 2 long aesthetascs. Antenna ( Fig. 1 A, B, G) with stout basicerite bearing small acute tooth on distolateral margin. Fifth segment of antennal peduncle (carpocerite) cylindrical, far falling short of midlength of antennal scale. Antennal scale about 0.4 of carapace length, 2.8 times longer than wide, lateral margin straight; distolateral tooth moderately strong, slightly overreaching rounded distal lamella. Flagellum exceeding twice length of body. Mandible (left) ( Fig. 2 A) with small 2-articulated palp, distal article subequal to proximal article, with 1 short terminal seta; molar process robust, truncate distally, with 3 principal peripheral teeth; incisor process large, armed with 3 unequal teeth distally. Maxillule ( Fig. 2 B) with palp deeply bilobed, outer lobe tapering distally; inner lobe short, strongly curved inward, with minute apical seta ( Fig. 2 C); proximal endite extending as far as distal endite, slightly tapering to roundly truncate tip, bearing stiff setae distally; distal endite subrectangular, with double row of spines and stiff setae on truncate distal margin. Maxilla damaged during dissection (not figured). First maxilliped ( Fig. 2 D) with proximal endite somewhat thickened, mesial margin doubled; basial endite suboval, separated from proximal endite by shallow notch followed by transverse suture; endopod relatively wide, tapering distally, far falling short of distal margin of distal endite; exopod well developed, with long flagellum, caridean lobe moderately broad; epipod slightly bilobed. Second maxilliped ( Fig. 2 E) with dactylus and propodus clearly separated; mesial margin of dactylus with numerous stiff setae; propodus with row of moderately long stiff setae on mesial margin; ischium and basis fused; coxa with convex mesial margin; exopod moderately long; epipod moderately large, subrectangular, without podobranch. Third maxilliped ( Fig. 2 F) with endopod moderately slender, not reaching distal margin of antennal scale; coxa ( Figure 2 G) with oval lateral plate (= epipod) and small setose tubercle on mesial margin; basis short, partially fused to ischiomerus; ischiomerus somewhat bowed in dorsal view, slightly tapering distally; carpus about 0.7 length of ischiomerus, about 4.9 times longer than high; ultimate segment 0.7 length of carpus, 4.9 times longer than high, tapering distally, with long terminal unguis and numerous stiff setae on mesial face; exopod well developed, reaching distal end of ischiomerus; single arthrobranch poorly lamellate, bud-like. First pereopod ( Fig. 3 A) slender, reaching distal margin of antennal scale by mero-carpal articulation. Chela ( Fig. 3 B, C) 4.4 times longer than broad; dactylus about 1.2 of palm length; cutting edges of fingers entire, forming thin edge; palm subcylindrical. Carpus 1.2 length of chela, 7.3 times longer than wide. Merus subequal in length to carpus. Ischium 0.7 length of merus. Grooming apparatus consisting of some short transverse rows of setae on proximomesial portion of palm and transverse row of short setae plus tuft of long setae located near ventromesial distal angle of carpus ( Fig. 3 B). Second pereopods ( Fig. 3 D) subequal, similar, moderately slender, overreaching distal margin of antennal scale by 0.2 length of merus. Chela ( Fig. 3 E) 1.4 of carapace length, 5.9 times longer than wide in dorsal view; surfaces smooth and glabrous. Dactylus slender, 1.2 length of palm, terminating in curved, acute tip; fixed finger similarly slender, slightly deflexed, terminating in curved, acute tip crossing tip of dactylus; cutting edges of both fingers forming thin plate, without conspicuous teeth. Palm subcylindrical, slightly swollen, 2.8 times longer than wide. Carpus slightly widened distally, 0.70 of chela length, 1.7 length of merus, 6.5 times longer than high; surfaces smooth. Merus 6.8 times longer than high. Ischium slightly shorter than merus. Ambulatory legs (third to fifth pereopods) slender compared with two other congeneric species. Third pereopod ( Fig. 3 F) overreaching distal margin of antennal scale by full length of propodus; dactylus ( Fig. 3 G) simple, compressed laterally, feebly curved, 0.25 of propodal length, 7.5 times longer than high, unguis not clearly demarcated, with tuft of short setae on extensor margin slightly distal to midlength; propodus with 4 widely spaced spinules on flexor margin, including 1 pair on distal margin; carpus 0.7 of propodal length; merus about 16 times longer than high; ischium 0.6 of meral length. Fourth pereopod ( Fig. 3 H, I) overreaching distal margin of antennal scale by 0.7 length of propodus, similar to third pereopod. Fifth pereopod ( Fig. 3 J, K) generally similar to third and fourth pereopods, but longer than them, overreaching distal margin of antennal scale by 0.7 length of propodus. FIGURE 1. Eupontonia gracilipes n. sp. , holotype, female (cl 3.2 mm), CBM-ZC 12300. A, carapace and cephalic appendages, lateral view (antennular flagella partially omitted; labrum shown); B, anterior part of carapace and cephalic appendages, dorsal view; C, fourth and fifth thoracic sternites, ventral view; D, pleon, lateral view; E, telson, dorsal view; F, bifurcated part of outer flagellum of left antennule; G, left antenna, ventral view (flagellum and marginal setae on antennal scale omitted); H, posterolateral tooth and spines of exopod of left uropod, dorsal view (setae omitted). Scale bars: 1 mm for A, D; 0.5 mm for B, C, E–H. FIGURE 2. Eupontonia gracilipes n. sp. , holotype, female (cl 3.2 mm), CBM-ZC 12300. Left appendages. A, mandible, inner view; B, maxillule, outer view; C, same, close up of distal part of palp, inner view; D, first maxilliped, outer view; E, second maxilliped, outer view; F, third maxilliped, lateral (outer) view; G, same, coxa, dorsal view; H, first pleopod, dorsal view (setae omitted); second pleopod, dorsal view (setae omitted). Scale bars: 0.5 mm. Protopods of pleopods slender. First pleopod ( Fig. 2 H) with endopod about 0.40 length of exopod, moderately narrow. Second to fifth pleopods each with appendix interna arising at about midlength of endopod (cf. Fig. 2 I). Uropod ( Fig. 1 D) with protopod bearing small acute posterolateral tooth. Exopod distinctly overreaching tip of telson (except for terminal spines), with submarginal row of setae along lateral margin; lateral margin nearly straight, terminating in small acute tooth, with 2 small movable spines just mesial to posterolateral tooth ( Fig. 1 H). Endopod slightly shorter than exopod. Coloration in life. Body and appendages entirely translucent. Corneas darkly pigmented. See Fig. 4 . Distribution. Known only from Ishigaki Island, Yaeyama Islands, southern Ryukyu Islands, at a depth of 5 m . Habitat. The unique holotype was found under coral rubble. No symbiotic association with other invertebrates was seen. FIGURE 3. Eupontonia gracilipes n. sp. , holotype, female (cl 3.2 mm), CBM-ZC 12300. A, left first pereopod, lateral view; B, same, chela, extensor view; C, same, mesial view; D, left second pereopod, lateral view; E, same, chela, extensor view; F, left third pereopod, lateral view; G, same, dactylus, lateral view; H, left fourth pereopod, lateral view; I, same, dactylus, lateral view; J, right fifth pereopod, lateral view; K, same, dactylus and distal part of propodus, mesial view. Scale bars: 1 mm for A, D, F, H, J; 0.5 mm for B, C, G, I, K. FIGURE 4. Eupontonia gracilipes n. sp. , holotype, female (cl 3.2 mm), CBM-ZC 12300, habitus in situ, photo taken by R. Minemizu. Remarks. The holotype was externally infested by an unidentified isopod parasite, which was attached to the right side of the carapace ( Fig. 4 ), although the parasite specimen was not preserved. The right first pleuron is modified to form an expanded fold to receive the anterior part of the parasite body. The present new species is readily distinguished from the other two congeneric species, E. noctalbata and E. oahu , by the presence of a distinct postrostral median ridge on the carapace, extending to the midlength of the carapace, and of a postrostral median tooth located at about anterior 0.1 of the carapace. In the latter two species, there is no postrostral median ridge and no postrostral tooth on the carapace ( Bruce 1971 : figs. 2, 3a, b; 2010: fig. 1A, C). Furthermore, ambulatory legs are comparatively slenderer in E. gracilipes n. sp. than in the latter two species (cf. Bruce 1971 : fig. 5h; 2010: fig. 3D, E). The lack of a supraorbital tooth on the carapace and the rounded posterior margin of the telson also distinguish E. gracilipes n. sp. from E. noctalbata . In E. noctalbata , the carapace is provided with a pair of supraorbital teeth ( Bruce 1971 : fig. 3a, b); the posterior margin of the telson is acutely pointed at the apex ( Bruce 1971 : fig. 3c; Li 1997 : fig. 7g ). The elongate, unarmed carpus of the second pereopods, which is distinctly longer than the palm of the chela, further separates E. gracilipes n. sp. from E. oahu . In E. oahu , the carpus of the second pereopod is much shorter than the palm and is armed with a small distomesial tooth (cf. Bruce 2010 : fig. 4A, D). As mentioned above, E. oahu is associated with a scleractinian coral Pocillopora meandrina (cf. Bruce 2010 ). In contrast, there is no evidence of a symbiotic association for E. noctalbata and E. gracilipes sp. nov. , although the holotype of E. noctalbata was discovered when a colony of the coral Galaxea fascicularis (Linnaeus, 1767) was removed ( Bruce 1971 ). Bruce (1971) considered that E. noctalbata was a free-living species. As mentioned above, the holotype of E. gracilipes n. sp. was found under coral rubble, suggesting that the new species is also freeliving. The dorsolateral spines on the telson in the holotype of E. gracilipes n. sp. are markedly asymmetrical in their arrangement (the left has one spine and the right has two spines) and are considered to be abnormal. It is probable that two pairs of dorsolateral spines are normally present, as in vast majority of pontoniine species. In fact, the nontype specimen of E. noctalbata reported by Li (1997) and specimens of the congeneric E. oahu have two pairs of dorsolateral spines on the telson ( Bruce 2010 ). Etymology. From the combination of the Latin, gracilis (= slender) and pes (= leg), in reference to the slender ambulatory legs (third to fifth pereopods). Used as a noun in apposition.