Eualus kikuchii Miyake & Hayashi, 1967

Komai, Tomoyuki & Fujiwara, Yoshihiro, 2012, Description of a new species of the hippolytid shrimp genus Eualus Thallwitz, 1892 from Japan, and clarification of the status of E. kikuchii Miyake & Hayashi, 1967 (Crustacea: Decapoda: Caridea), Zootaxa 3546, pp. 68-80 : 74-79

Eualus kikuchii Miyake & Hayashi, 1967

( Figs 6–8 )

Eualus kikuchii Miyake & Hayashi, 1967: 261 , figs 6, 7; Hayashi & Miyake 1968: 129, fig. 4; Noël 1978: 32 (key); Chace 1997: 43 (list); De Grave & Fransen 2010: 417 (list).

Eualus bulychevae .— Miyake 1982: 184 (part; list); Hayashi 1993: 311, figs 244a, 245a; Komai & Hayashi 2002: 390 (list). Eualus sp. cf. kikuchii .— Fujiwara et al. 2007: 223 (list; part).

Material examined. Holotype. Tomioka Bay, Amakusa Islands, Kyushu, 21 April 1964, coll. T. Kikuchi, male (cl 1.8 mm), KMNH-ZLKU 8072.

Non-type. Off Uze, Amakusa, Kyushu, 45 m, 14 April 1964, dredge, coll. T. Kikuchi, 1 male (cl 1.5 mm), 3 females (cl 1.4–2.4 mm), 7 ovigerous females (cl 1.9–2.4 mm), KMNH-ZLKU 8406. RV Tansei-maru, KT95-5 cruise, stn TB18-1, Okinoyama Bank, Sagami Sea, 34°58.7’N, 139° 40.0E, 102–103 m, 21 April 1995, dredge, coll. T. Komai, 1 female (cl 2.4 mm), CBM-ZC 1821. TRV Shin’yo-maru, 1996 cruise, stn 7, Takase Bank, Izu Islands, 34°26.80’N, 139°11.17’E, 87–93 m, 23 October 1996, dredge, 1 ovigerous female (cl 2.2 mm), coli. T. Komai, CBM-ZC 4629. Sagami Bay, off Arasaki, Miura, 35°11.02’N, 139°34.55’E, 60–67 m, 8 March 2002, commercial gill net, coll. T. Komai, 1 male (cl 1.4 mm), 1 female (cl 2.2 mm), CBM-ZC 10334; same locality, 35°10.53’N, 139°34.56’E, 62–73 m, 8 March 2002, commercial gill net, coll. T. Komai, 1 male (cl 1.8 mm), 3 females (cl 1.8–1.9 mm), 3 ovigerous females (cl 1.7–2.3 mm), CBM-ZC 10336. RV Natsushima , NT05-12 cruise (leg 1), ROV Hyper-Dolphin, dive #452, off Cape Nomamisaki, Kagoshima Prefecture, 31°21.000’N, 129°59.160’E, 227 m, 27 July 2005, manipulator, 1 ovigerous female (cl 2.8 mm), JAMSTEC 20050033423; same data, 1 male (cl 1.7 mm), JAMSTEC 20050033424; RV Natsushima , NT07-09 cruise, ROV Hyper-Dolphin, dive #869, same locality, 8 June 2007, manipulator, 2 ovigerous females (cl 2.7, 3.0 mm), JAMSTEC 071997 – 071998.

Redescription. Female. Body ( Fig. 6 ) moderately stout for genus. Rostrum ( Fig. 7 A, B) 0.5–0.6 length of carapace, almost straight, directed forward or downward, reaching or slightly falling short of distal margin of first segment of antennular peduncle, fairly broadened proximally; dorsal margin slightly sloping anteriorly, armed with 4–6 teeth (posteriormost tooth located just above orbital margin or slightly posterior to orbital margin); ventral margin not forming limb or blade, unarmed or armed with 1 (rarely 2) tiny subterminal tooth; no conspicuous lateral carina. Carapace ( Fig. 7 A, B) with dorsal margin slightly convex, rostral carina reaching or slightly extending beyond rostral base; antennal tooth moderately strong; inferior orbital angle obtuse, not clearly separated from antennal tooth; pterygostomial tooth tiny, but always present at least in females; anterolateral margin between antennal and pterygostomial teeth convex.

Abdomen ( Fig. 6 ) rounded dorsally. Posterodorsal margin of third tergite moderately produced, unarmed. Fourth and fifth pleura each with sharp posteroventral tooth. Sixth somite 1.6–1.7 times longer than fifth, 1.9–2.0 times longer than high; posterolateral tooth terminating in acute tooth; small posteroventral tooth present. Telson ( Fig. 7 C) about 1.4 times longer than sixth abdominal somite, about 3.0 times longer than anterior width; lateral margins parallel in anterior 0.4, tapering thereafter to convex posterior margin; dorsal surface with 4 or 5 pairs of dorsolateral spines (excluding 1 pair at posterolateral corner); posterior margin with 2 pairs of spines (mesial pair more than 4 times longer than lateral pair) and 1 mesial pair of stiff setulose setae.

Eye ( Figs 6 , 7 B) subpyriform; cornea bearing ocellar spot, its maximal width about 0.3 of carapace.

Antennular peduncle ( Fig. 7 A, B) reaching distal 0.3–0.4 of antennal scale. Basal segment reaching nearly to midlength of antennal scale, armed with 1 strong distolateral tooth; ventromesial ridge with prominent tooth subdistally; stylocerite just reaching level of distal margin of basal segment, terminating in acute, slender tooth, without proximolateral process. Distal two segments combined much shorter than basal segment, each with distinct spiniform distal tooth.

Antennal peduncle ( Fig. 7 A, B) with basicerite bearing small ventrolateral distal tooth, dorsolateral distal angle rounded. Carpocerite slightly falling short of midlength of antennal scale. Antennal scale 0.7–0.8 times as long as carapace, about 2.6 times longer than wide; lateral margin nearly straight; distolateral tooth slightly falling short of or just reaching rounded distal margin of blade.

Mouthparts not dissected. Third maxilliped ( Fig. 8 A) moderately long and slender, overreaching antennal scale by 0.3–0.5 length of ultimate segment; ultimate segment 2.8 times longer than penultimate segment (= carpus), tapering distally, distal part bearing some small spines; antepenultimate segment shorter than distal two segments combined, narrowing proximally, dorsodistal margin with tiny tooth, distolateral margin with small spine-like tooth and long stout seta just inferior to base of tooth. Coxa with strap-like, terminally hooked epipod.

Strap-like, terminally hooked epipods on first to third pereopods.

First pereopod ( Fig. 8 B) moderately stout, not reaching distal margin of antennal scale. Chela about 1.5 times longer than carpus, about 3.5 times longer than wide; dactylus about 0.6 times as long as palm, with 2 terminal claws; palm subcylindrical, fixed finger terminating in single claw. Merus with minute spinules on ventral margin proximally. Ischium also with minute spinules on ventral margin distally.

Second pereopod ( Fig. 8 C) overreaching antennal scale by length of chela and half of carpus; carpus divided into 7 articles.

Third to fifth pereopods moderately long and slender, similar in general structure. Third pereopod ( Fig. 8 D) overreaching antennal scale by about 0.4 length of propodus; dactylus slightly less than 0.3 times as long as propodus, about 3.0 times longer than high, armed with 4–6 accessory spines over entire length of flexor margin ( Fig. 8 E); propodus with row of spinules on flexor margin; carpus about half length of propodus; merus with 2 or 3 lateral spines located in distal one-third; ischium not particularly widened distally. Fourth pereopod ( Fig. 8 F) overreaching antennal scale by 0.2–0.3 length of propodus; merus with 1–3 lateral spines located in distal 0.3. Fifth pereopod (fig. 8G) reaching to distal margin of antennal scale by dactylus; merus unarmed or armed with 1 spine located subdistally.

Pleopods without distinctive features. Uropodal protopod with posterolateral tooth gradually tapering; both rami slightly overreaching posterior top of telson.

Males. Generally similar to females. Rostrum shorter, usually falling short of distal margin of first segment of antennular peduncle. Third and fourth pereopods similar to those of females, not showing sexual dimorphism in armature of merus. Endopod of first pleopod ( Fig. 7 D) with appendix interna tapering distally, mesial subdistal lobe angular. Endopod of second pleopod ( Fig. 7 E) with appendix masculina slightly shorter than appendix interna, slightly broadened distally, bearing several long stiff setae.

Coloration in life. Body and appendages generally translucent.

Distribution. Known only from the Pacific side of Japanese mainland, from Sagami Sea to Amakusa, Kyushu, 60– 227 m.

Remarks. Eualus kikuchii was originally described on the basis of six specimens from Amakusa, Kyushu, Japan ( Miyake & Hayashi 1967). However, Miyake (1982: 184) regarded this taxon as a junior synonym of E. bulychevae , described on the basis of material from the South Kuril Strait, Kuril Islands, but he gave no comments to potentially justifying this action. Later Hayashi (1993) supported Miyake’s (1982) synonymy, and noted that there were no significant morphological differences between the type series of E. kikuchii and the original description of E. bulychevae . On the other hand, Chace (1997) and De Grave & Fransen (2010) listed E. kikuchii as a valid species, though no comments were given.

During this study, we compared material from various sources, including the holotype and topotypic material from Amakusa, and the original description of E. bulychevae by Kobjakova (1955). The type material of E. bulychevae may have been deposited in the Zoological Institute, St. Petersburg, but no information as such has been forthcoming. We are now convinced that E. kikuchii is a valid species, distinguished morphologically from E. bulychevae , as follows: (1) the rostrum is relatively shorter in E. kikuchii than in E. bulychevae (slightly falling short of or reaching the first segment of the antennular peduncle in E. kikuchii versus reaching to the second segment of the antennular peduncle in E. bulychevae ; (2) the carapace is provided with a small pterygostomial tooth in E. kikuchii , whereas there is no tooth at the pterygostomial angle in E. bulychevae ; (3) the postrostral median carina does not reach beyond the rostral base in E. kikuchii , whereas it reaches beyond the midlength of the carapace in E. bulychevae ; (4) the stylocerite reaches the distal margin of the first segment of the antennular peduncle in E. kikuchii , rather than falling short of it in E. bulychevae . Furthermore, in spite of recent colleting activities in northern Japan, no specimens referable to E. kikuchii have been collected, suggesting that this species is restricted to the southwestern part of Japanese mainland and its adjacent waters.

Kobjakova (1955) mentioned one ovigerous female specimen that differed from other specimens in the proportionally longer rostrum reaching to the distal end of the antennal peduncle, though she assigned this specimen to E. bulychevae . It is likely that this specimen might actually represent a species other than E. bulychevae .

Among the species characterized by the possession of epipods on the anterior three pairs of pereopods, E. dozei ( A. Milne-Edwards, 1891) known from Chile and E. pusiolus ( Krøyer, 1841) from the northern North Pacific and the northern North Atlantic are similar to E. kikuchii . Shared characters are: rostrum comparatively short, with posteriormost dorsal tooth rostral or slightly postrostral; ventral margin of rostrum unarmed or at most two subterminal teeth; carapace with pterygostomial tooth. Eualus kikuchii is distinguished from both E. dozei and E. pusiolus by the possession of two or three distolateral spines, instead of only a single spine ( Holthuis 1952; Komai & Yakovlev 2000) on the merus of the third pereopod. Eualus dozei further differs from E. kikuchii in the longer stylocerite, distinctly overreaching the distal margin of the first segment of the antennular peduncle ( Holthuis 1952) vs. in E. kikuchii the stylocerite reaching or falling short of margin. Eualus pusiolus further differs from E. kikuchii in the following characters ( Komai & Yakovlev 2000; d’Udekem d’Acoz & Wirtz 2002): (1) rostrum reaching to the distal margin of the first segment of the antennular peduncle in E. kikuchii vs. falling short in E. pusiolus ; four to six dorsal rostral spines in E. kikuchii versus less than four in E. pusiolus ; lateral rostral carina poorly developed in E. kikuchii versus sharply defined, extending onto gastric region of carapace in E. pusiolus and inferior orbital angle rounded in E. kikuchii versus but distinct, triangular lobe in E. pusiolus .

Figures

FIGURE 6. Eualus kikuchii Miyake & Hayashi, 1967, ovigerous female (cl 3.0 mm), JAMSTEC 071997 – 071998, habitus. Scale bar: 2 mm.

FIGURE 7. Eualus kikuchii Miyake & Hayashi, 1967. A, B, ovigerous female (cl 2.4 mm), KMNH - ZLKU 8406; C, ovigerous female (cl 3.0 mm), JAMSTEC 071997 – 071998; male (cl 1.7 mm), JAMSTEC 20050033424. A, carapace and antennae, lateral view (inner flagellum of antennule and antennal flagellum damaged); B, anterior part of carapace and cephalic appendages (antennular flagella omitted; left eye removed; setae partially omitted); C, telson, dorsal view; D, endopod of left first pleopod, ventral view; E, endopod of second pleopod, ventral view. Scale bars: 1 mm for A – C; 0.25 mm for D, E.

FIGURE 8. Eualus kikuchii Miyake & Hayashi, 1967. ovigerous female (cl 2.4 mm), KMNH-ZLKU 8406. A, right third maxilliped, lateral view; B, left first pereopod, lateral view; C, left second pereopod, lateral view; D, left third pereopod, lateral view; E, same, dactylus, lateral view; F, left fourth pereopod, lateral view; G, left fifth pereopod, lateral view. Scale bars: 1 mm for A – D, F, G; 0.5 mm for E.