Eualus ctenomerus Komai & Fujiwara, 2012, n. sp.

Eualus ctenomerus n. sp.

(Figs 1–5)

Eualus sp. cf. kikuchii.— Fujiwara et al. 2007: 223 (list; part).

Material examined. Holotype: RV Natsushima, NT07-09 cruise, ROV Hyper-Dolphin, dive #869, off Cape Nomamisaki, Kagoshima Prefecture, 31°21.000’N, 129°59.160’E, 227 m, 8 June 2007, manipulator, male (cl 1.8 mm), NSMT-Cr 22239 (formerly JAMSTEC 071992).

Paratypes: RV Natsushima, NT05-12 cruise (leg 1), ROV Hyper-Dolphin, dive #453, off Cape Nomamisaki, Kagoshima Prefecture, 31°21.000’N, 129°59.160’E, 227 m, 27 July 2005, suction sampler, 1 male (cl 1.6 mm), JAMSTEC 20050033425; same data as holotype, 3 ovigerous females (cl 3.0– 3.1 mm), JAMSTEC 071994 – 071996.

Non-type: TRV Toyoshio-maru, 1996-5 cruise, stn 11, S of Yakushima Island, Ohsumi Islands, 30°12.00’N, 125°46.0’E, 135 m, 4 June 1996, sledge, coll. T. Komai, 1 male (cl 1.4 mm), CBM-ZC 4060.

Description. Male holotype. Body (Fig. 1) moderately stout for genus. Rostrum (Fig. 2 A, B) 0.5–0.6 length of carapace, nearly straight, spiniform, directed forward, far falling short of distal margin of first segment of antennular peduncle; basal part moderately widened; dorsal margin armed with 3 teeth, distal 0.2 unarmed; ventral margin with minute subterminal tooth; no conspicuous lateral carina. Carapace (Fig. 2 A) with dorsal margin nearly straight, rostral carina reaching slightly beyond orbital margins; antennal tooth moderately strong; inferior orbital angle obtuse, not clearly separated from antennal tooth; pterygostomial margin rounded; anterolateral margin between antennal and pterygostomial teeth slightly sinuous.

Abdomen (Fig. 1) rounded dorsally. Posterodorsal margin of third tergite moderately produced. Fourth and fifth pleura each with small posteroventral tooth. Sixth somite 1.8 times longer than fifth, 1.8 times longer than high; posterolateral tooth terminating in acute tooth; small posteroventral tooth present. Telson (Fig. 2 C) about 1.3 times longer than sixth abdominal somite, about 3.5 times longer than anterior width; lateral margins parallel in anterior 0.4, narrowing thereafter to convex posterior margin; dorsal surface with 4 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 1, 2 B) subpyriform; cornea bearing ocellar spot, its maximal width about 0.4 of carapace length.

Antennular peduncle (Fig. 2 B) reaching distal 0.3 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 reaching or slightly falling short of distal margin of basal segment, terminating in acute tooth, without proximolateral process. Distal two segments combined much shorter than basal segment, each with distinct spiniform distal tooth. Outer flagellum with thickened aesthetasc-bearing portion subequal in length to carapace. Inner flagellum elongate, about twice length of outer flagellum.

Antennal peduncle (Figs 1, 2 B) with basicerite bearing small ventrolateral distal tooth, dorsolateral distal angle rounded. Carpocerite nearly reaching midlength of antennal scale. Antennal scale 1.1 times longer than carapace, 2.9 times longer than wide; lateral margin faintly convex; distolateral tooth slightly falling short of rounded distal margin of blade.

Mouthparts not dissected. Third maxilliped (Fig. 3 A) moderately long and slender, overreaching antennal scale by about 0.4 length of ultimate segment; ultimate segment 2.7 times longer than penultimate segment (= carpus), tapering distally, distal part bearing some small spines; antepenultimate segment subequal in length to distal two segments combined, slightly narrowing proximally, dorsodistal margin unarmed, 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. 3 B) moderately stout, far falling short of distal margin of antennal scale. Chela about 1.4 times longer than carpus, 4.3 times longer than wide; dactylus about 0.7 times as long as palm, with 2 terminal claws; palm subcylindrical, fixed finger terminating in single claw. Merus with short row of minute spinules on ventral margin proximally. Ischium without minute spinules on ventral margin.

Second pereopod (Fig. 3 C) overreaching antennal scale by 0.4 length of carpus; carpus divided into 7 articles. Third to fifth pereopods moderately long and slender, similar in general structure and armature. Third pereopod (Fig. 3 D) overreaching antennal scale by about 0.4 length of propodus; dactylus slightly more than 0.2 times as long as propodus, about 3.0 times longer than high, armed with 4 accessory spines on over entire length of flexor margin (Fig. 3 E); propodus with few slender spinules on flexor margin distally; carpus about half length of propodus; merus somewhat compressed laterally, widest slightly distal to midlength, with comb-like row of closely set spines (about 20 in number) ventrolaterally in distal 0.4, without row of setae on lateral surface adjacent to comb-like spine series; ischium distinctly widened distally. Fourth pereopod (Fig. 3 G) overreaching antennal scale by 0.2 length of propodus. Fifth pereopod (Fig. 3 H) reaching to distal margin of antennal scale by dactylus; dactylus about 0.2 times as long as propodus; propodus with row of slender spinules on entire length of flexor margin; merus with 5 well spaced small ventrolateral spines arranged in short row in distal 0.3; ischium not particularly widened distally.

Endopod of first pleopod (Fig. 2 E) with appendix interna tapering distally, mesial subdistal lobe obsolescent. Endopod of second pleopod (Fig. 2 F) with appendix masculina stout (about twice as long as wide), only about onethird length of appendix interna, bearing several long stiff setae. Uropodal protopod with posterolateral tooth gradually tapering; both rami slightly overreaching posterior tip of telson.

Paratype male. Very similar to holotype male except for following: rostrum with 4 dorsal teeth, ventral margin unarmed; merus of fifth pereopod unarmed.

Females. Body stouter than in males (Fig. 4). Rostrum (Fig. 5 A) straight or slightly curved dorsally, 0.5–0.6 times as long as carapace, with 3 or 4 teeth in proximal half, distal half unarmed; ventral margin unarmed or armed with 1 tiny subterminal tooth. Carapace (Fig. 5 A) with dorsal margin slightly convex. Third and fourth pereopods normal (Fig. 5 B, C); meri subcylindrical, with 3 or 4 (third) and 2 or 3 (fourth) lateral spines located in distal 0.2–0.3. Merus of fifth pereopod unarmed or armed with 1 ventrolateral distal spine (Fig. 5 D). Pleopods without distinctive features.

Coloration in life. Not known.

Distribution. Off southern Kyushu, Japan; 135– 227 m.

Remarks. This new species is characterized by the possession of epipods on the anterior three pairs of pereopods, the rounded pterygostomial angle of the carapace and the male with meri of the third and fourth pereopods bearing a row of closely set spines in a comb-like arrangement. As such, it appears closest to E. cteniferus known only from Algoa Bay, Durban, South Africa; E. drachi known only from the Mediterranean; and E. pectiniformis known only from southeastern Australia (Barnard 1950; Noel 1978; Hanamura 2008). Eualus ctenomerus n. sp. can be distinguished from E. cteniferus, by the following characters: (1) the ventral margin of the rostrum is unarmed or armed with a single subterminal tooth in E. ctenomerus, rather than bearing two or three ventral teeth in E. cteniferus (cf. Barnard 1950; Kensley 1972); (2) all dorsal rostral teeth are placed on the rostrum proper in E. ctenomerus, whereas the posteriormost tooth is located posterior to the level of orbital margin (postrostral) in E. cteniferus (cf. Barnard 1950; Hanamura 2008).

From E. drachi, the new species can be distinguished by the following characters (Noël 1978; d’Udekem d’Acoz & Wirtz 2002): (1) the rostrum is relatively short, not reaching beyond the distal margin of the first segment of the antennular peduncle in E. ctenomerus, rather than reaching to the distal margin of the second segment in E. drachi; (2) the dorsal rostral teeth are all placed on the rostrum proper in E. ctenomerus, whereas the posteriormost tooth is postrostral in E. drachi; (3) the ischium of the first pereopods is unarmed ventrally in E. ctenomerus, rather than having a few minute spinules on the ventral surface distally in E. drachi.

Eualus pectiniformis is very similar to the present new species, but the following minor differences could differentiate these two taxa: (1) the merus of the first pereopod lacks a proximolateral process in E. ctenomerus, though a small but distinct proximal process on the lateral surface of the segment is present in E. pectiniformes (cf. Hanamura 2008: fig. 2i); (2) spines comprising the comb-like row on the merus of the third pereopod in males are proportionally longer in the new species than in E. pectiniformes (cf. Fig. 3 D, F and Hanamura 2008: fig. 3b); (3) the merus of the third pereopod is glabrous in E. ctenomerus (Fig. 3 D), whereas it bears a short row of setae on the lateral surface adjacent to comb-like spine series on the ventrolateral margin (Hanamura 2008: fig. 3b).

Eualus lebourae Holthuis, 1951, known from the eastern Atlantic and Azores, is also closely similar to the abovementioned species, though no morphological information on the male is available so far. d’Udekem d’Acoz & Wirtz (2002) suspected that E. drachi might be a geographical variant of E. lebourae. Eualus ctenomerus n. sp. can be distinguished from E. lebourae by the following minor points (cf. Holthuis 1951; Crosnier & Forest 1973): (1) the rostrum does not overreach the distal margin of the first segment of the antennular peduncle in E. ctenomerus, rather than overreaching it in E. lebourae; (2) the posterior margin of the telson is rounded in E. ctenomerus, but in E. lebourae, it bears a sharp median tooth; (3) the stylocerite reaches or slightly falls short of the distal margin of the first segment of the antennular peduncle in E. ctenomerus, rather than somewhat overreaching it in E. lebourae.

In the presence of a comb-like row of spines on the meri of the third and fourth pereopods in the male and the possession of epipods on the anterior three pairs of pereopods, Eualus butleri Jensen, 2004, known from Alaska to Puget Sound is also similar to this new species. Nevertheless, the presence of a pterygostomial tooth on the carapace, the short stylocerite (far falling short of the first segment of the antennular peduncle) and the comb-like spinules extending over the entire length of the merus of the third pereopod immediately distinguish E. butleri from E. ctenomerus (cf. Jensen 2004).

The characteristic comb-like row of spines on the meri of the third and fourth pereopods in the male is also seen in E. cranchii (Leach, 1817) and E. occultus (Lebour, 1936), both known from the northeastern Atlantic. However, these two species are readily distinguished from E. ctenomerus and other related species in the lack of an epipod on the third pereopod (Holthuis 1951; d’Udekem d’Acoz & Wirtz 2002).

Etymology. From the combination of the Greek “kteis” (= comb) “merus” (= femur), in reference to the comblike spines on the meri of the third and fourth pereopods.