(Figs. 1 –4, 16 A)
Hippolyte commensalis. — Holthuis, 1995: 146 (part) [not Kemp, 1925]. Hippolytidae sp. — Kato & Okuno, 2001: 57, unnumbered fig.
Material examined. Japan: holotype, ovigerous female (pcl. 2.0 mm, tl. 10.5 mm) (CMNH –ZC 02397), Izu Islands, Hachijo-jima Island, Yaene Fishing Port, 5 m, from Stereonephthea japonica, coll. S. Kato, 0 5 Dec. 2000. Indonesia: 1 ovigerous female (pcl. 1.4 mm) (CMNH –ZC 02214), NW of Bali Island, Menjagan Islet, 10 m, from unidentified nephtheiid host, coll. T. Yanagisawa, 0 3 Sept. 2006. Australia: 1 female (pcl. 1.5 mm, tl. 7.5 mm) (QM W 33474), Great Barrier Reef, Lizard Island, lagoon, patch reef, LI 10 -037, 14 ° 41.202 ’S 145 ° 27.307 ’E, 6–8 m, on Efflatounaria sp., coll. I. Marin, 30 Aug. 2010.
Description. Holotype female. Carapace smooth, swollen, gibbous dorsally and with several scattered tufts of plumose setae (Figs. 1 B); supraorbital, antennal and hepatic teeth present; antennal tooth sharp, situated just below orbital angle; hepatic tooth sharp, situated below and slightly behind level of antennal tooth, subequal to antennal tooth, slightly exceeding distal margin of carapace. Rostrum long, compressed, dorsally unarmed and slightly convex at medial part, smooth; ventrally armed with single subapical tooth; proximal lateral rostral lamina well developed, bearing sharp supraorbital tooth above level of proximal orbital margin (Fig. 2 B, C). Orbit well developed, inferior orbital angle slightly produced distally. Pterygostomial angle bluntly projected.
Abdominal somites smooth and unarmed; dorsal surface of abdominal somites I–V covered with several tufts of plumose setae; pleura of abdominal somites I–V rounded (Fig. 1). Telson (Fig. 2 D) relatively stout, about twice longer than proximal width, narrowing posteriorly, with 2 pairs of small dorsal submarginal spines at 0.6 and 0.8 of telson length. Distal margin of telson armed with 4 pairs of spines including pair of short stout lateral spines.
Eyes (Fig. 2 E) normal, well developed; eyestalk subcylindrical, slightly wider than long; cornea subovate, without papilla.
Antennule (Fig. 2 F) well developed; basal segment about 1.5 times as long as wide, ventromedial tooth absent, distolateral angle armed with acute distolateral tooth reaching distal margin of intermediate segment, inner distolateral angle with several long plumose setae; stylocerite well developed, sharp, reaching distal margin of basal segment; intermediate segment stout, about 1.5 times wider than long, with slightly convex inner margin bearing long plumose setae; distal segment stout, about as long as wide, with long plumose setae along inner margin; proximal part of upper flagellum with 5 segments, shorter ramus with 1 stout segment.
Antenna (Fig. 2 G) normal, well developed; basicerite armed with blunt triangular tooth distoventrally, slightly overreaching distal margin of segment; carpocerite stout, about as long as wide, reaching midlength of scaphocerite; flagellum well developed; scaphocerite wide, about 1.5 times as long as maximal width, overreaching antennular peduncle, with well developed acute distolateral tooth.
Mandible robust (Fig. 3 A), without palp; incisor process reduced, slender, with sharp tip; molar process robust, with stout sharp distal teeth. Maxillule (Fig. 3 B) normal, with well developed bilobed palp, ventral lobe armed with long simple setae; upper lacinia wide, with convex ventral margin, flaring distally, with numerous stout setae along distoventral margin, bearing 2 or 3 long plumose setae at distodorsal angle; lower lacinia more slender, tapering distally, covered with long simple setae. Maxilla (Fig. 3 C) with simple blunt palp; endites completely fused, armed with stiff, short stout setae as well as some elongated plumose setae at distodorsal angle; scaphognathite well developed, fringed with plumose setae. Maxilliped I (Fig. 3 D) with completely fused endites, armed with short stout setae along distal margin as well as some elongated plumose setae at distodorsal angle; exopod well developed with well marked caridean lobe furnished with plumose setae; epipod rectangular, bilobed distally. Maxilliped II (Fig. 3 E) with well developed exopod; ischium stout, with long plumose setae along lateral margin; propodal segment short, length equal to dactylar segment, with convex dorsal margin furnished with long simple setae, ventral margin unarmed; dactylar segment convex, armed with numerous stout and long simple setae along distal margin; epipod well marked, distally bilobed. Maxilliped III (Fig. 3 F) large and very stout, overreaching scaphocerite and antennular peduncle; exopod reduced, extending to midlength of ischiomeral segment; ischiomeral segment about 3 times as long as wide, slightly tapering distally; penultimate segment about 2.5 times as long as wide, smooth; terminal segment with distal margin oblique, armed with row of strong spines distally; arthrobranch well developed.
Pereiopod I (Fig. 4 A) stout and unarmed; coxa with small arthrobranch; basis as long as wide, with small distoventral lobe; ischium about as long as wide, with long simple setae along ventral margin; merus about 1.5 times longer than wide; carpus shorter than merus, equal to the length of propodus, about as long as wide, flaring distally, distodorsal and lateral margins overlapping carpo-propodal articulation, with row of stout plumose setae along distoventral margin; palm (Fig. 4 B) about as long as wide, subcylindrical, swollen proximally, smooth; fingers stout, about half length of palm, subspatulate, nearly as long as wide, cutting edges with several large acute teeth.
Pereiopod II relatively slender, segments unarmed (Fig. 4 C); coxa as long as wide, with arthrobranch; basis about as long as wide, with curved lobe distoventrally; ischium about 1.5 times longer than wide, smooth; merus about 3.5 times as long as wide, margins straight; carpus subdivided into 3 segments with ratio of about 2: 1: 1.5; palm subcylindrical, slightly shorter than distal carpal segment, about as long as wide, with straight smooth margins; fingers robust, equal to length of palm, about 2.5 times as long as wide, subspatulate, cutting edges with several large acute teeth.
Pereiopods III–V (Figs. 4 D–F) similar, relatively slender, with segments unarmed except for propodi of pereiopods III and IV bearing single distoventral spine. Pereiopod III with basis about as long as wide; ischium about 3 times longer than wide, length equal to merus; merus about 3 times as long as wide, with straight margins, bearing large movable spine at distoventral angle; carpus about 3 times as long as maximal width, half as long as merus, flaring distally, with distodorsal margin overhanging carpo-propodal articulation; propodus about 5 times as long as wide, with smooth straight margins, with only distoventral angle armed with single small spine; dactylus slender, basal part about 1.5 times as long as maximal width, simple, unguis elongate and curved, without accessory tooth.
Pleopods normal. Uropods slender, slightly exceeding telson; distolateral margin of exopod without fixed tooth, with only slender movable spine (Figs. 2 H).
Coloration. General coloration similar to that of the host alcyonarian soft coral: carapace and abdomen with yellowish or pale white labyrinthine bands, interspaces dark green or pinkish white with numerous fine white spots. Sixth abdominal somite similar to the coloration of interspaces between labyrinthine bands, but with anterior part whitish. Anterior parts of telson and uropods whitish while posterior part dark green. Cornea pinkish or yellowish white, eyestalk completely white. Distal part of chelipeds dark green, gradually paler proximally. Ambulatory pereiopods whitish (Fig. 16 A).
Remarks. The present new species is very remarkable in having a strongly gibbous carapace. Other features that can be used to separate this species from the other species of the genus are: 1) wide lateral rostral lamina reaching almost to tip of rostrum; 2) shorter and less wide fingers of pereiopod I; 3) stouter ambulatory pereiopods and 4) stouter telson with dorsal spines situated close to its distal margin.
Host. The holotype from Hachijo-jima Island, Japan was associated with the soft coral Stereonephthea japonica Utinomi, 1954 (Octocarallia, Alcyonacea, Nephtheidae). The Indonesian specimen was collected from an unidentified nephtheiid soft coral, while the Australian specimen was collected from the soft coral Efflatounaria sp. (Octocarallia, Alcyonacea, Nephtheidae).
Etymology. The species is named after its characteristic gibbous carapace; dosennus (Latin) for humpback. The standard Japanese name for this species is Marumi-kakure-moebi.
Size. The largest collected specimen is an ovigerous female of pcl. 2.1 mm, tl. 10.5 mm.
Distribution. The present material was collected in Izu Islands of Japan, Bali of Indonesia and Lizard Island, northern part of the Great Barrier Reef of Australia. The gibbous, abnormal “ Hippolyte commensalis ” female specimen reported in Holthuis (1995) from the Gulf of Aqaba, Red Sea, very likely belongs to A. dossena sp. nov.