Lebbeus magnificus, Komai, Tomoyuki, 2015

Komai, Tomoyuki, 2015, Reinstatement and redescription of Lebbeus armatus (Owen, 1839), long synonymized with L. groenlandicus (Fabricius, 1775), and description of one new species from the southwestern Sea of Okhotsk, Hokkaido, Japan (Crustacea: Decapoda: Caridea: Thoridae), Zootaxa 3905 (4), pp. 451-473 : 464-471

Lebbeus magnificus n. sp.

( Figs. 9–13 )

Material examined. Holotype: Kitami-Yamato Bank, southwestern Sea of Okhotsk, Hokkaido, 44°52.6’N, 144°20.7’E, 156 m, 23 July 1992, otter trawl, ovigerous female (cl 24.0 mm) CBM-ZC 12597.

Paratypes: same data as holotype, 1 male (cl 17.7 mm), CBM-ZC 12598; same locality as holotype, 44°51.5’N, 144°20.8’E to 44°53.4’N, 144°20.8’E, 156 m, 4 September 1991, otter trawl, coll. T. Komai, 1 male (cl 19.5 mm), 1 female (cl 25.4 mm), CBM-ZC 12599; same locality, 44°30.1’N, 144°14.5’E, 208 m, otter trawl, coll. M. Yabe, 1 female (cl 20.5 mm), CBM-ZC 518.

Description. Females. Body ( Fig. 9 ) robust; integument firm, surface with sparse very short setae on lateral part of carapace and pleonal pleura; tips of spines or teeth darkly pigmented generally.

Rostrum (Figs. Figs. 9 , 10 A, B) slightly ascending and curving dorsally, reaching distal margin of second segment of antennular peduncle, 0.6–0.8 times as long as carapace; dorsal margin armed with 1 small tooth located at or slightly proximal to midlength, followed by 5 much stronger, crested teeth on middorsal carina of carapace (1 tooth sometimes located anterior to rostral base); ventral margin armed with 1–3 small teeth in distal 0.4, ventral lamina slightly developed, outline of ventral margin gently convex; lateral carina conspicuous in proximal 0.6, then fading away toward distal. Carapace ( Figs. 9 , 10 A–C) with high middorsal carina extending to posterior margin of carapace, posteriormost tooth much smaller than preceding 3 teeth, arising from 0.6 of carapace; dorsal outline in lateral view strongly convex; supraorbital tooth very strong, arising at rostral base, directed slightly upward in lateral view and slightly laterally in dorsal view, its dorsal margin carinate and fairly elevated (thus, surface between rostrum and supraorbital tooth forming deep channel), ventral margin slightly sinuous in lateral view; deep V-shaped notch just ventral to base of supraorbital tooth merging into orbit; suborbital lobe prominent, roundly triangular, with rounded sinus just mesial to blunt apex, inner margin crested ( Fig. 12 A); anterolateral margin between antennal and pterygostomial teeth strongly sinuous with concavity at base of antennal tooth; antennal tooth strong, reaching as far as suborbital lobe, distinctly buttressed; pterygostomial tooth weaker than antennal tooth, but still well developed, relatively slender; postorbital region deeply depressed; branchial ridge absent.

Pleon ( Figs. 9 , 10 D) dorsally rounded. First pleomere with anterolateral margin obtusely angular; pleuron with 2 small ventral teeth (ventral margin between teeth nearly straight or slightly concave). Second pleomere with deep transverse groove on tergum, posterior section slightly higher than anterior section; pleuron with small tooth at midpoint of ventral margin. Third pleomere with posterodorsal margin gently produced posteriorly; pleuron with small tooth at midpoint of ventral margin. Fourth pleuron with large posteroventral tooth. Fifth pleuron with 2 or 3 ventral teeth, including 1 strong posteroventral tooth and 1 or 2 smaller anteroventral teeth. Sixth pleomere 1.6 times as long as fifth pleomere and 1.7 times as long as high; posterodorsal margin slightly bilobed ( Fig. 10 E); posterolateral process terminating in slender tooth ( Fig. 12 B); posteroventral angle somewhat flared laterally, with large tooth. Telson ( Fig. 10 E) 1.6 times as long as sixth somite, 3.0 times longer than greatest width, tapering posteriorly to convex posterior margin from anterior one-fourth; dorsal surface deeply sulcate medially, proximally with prominent protuberance bearing tuft of short setae posteriorly; dorsolateral ridge distinct, with row of 6 or 7 spines on either side; posterior margin with 2 pairs of spines (mesial pair stronger than lateral pair) and median tuft of setae ( Fig. 10 F).

Eye ( Fig. 10 A, B) subpyriform with eyestalk narrowing proximally; cornea small, slightly wider than eyestalk, its maximum width 0.15 of carapace length; ocellus present.

Antennular peduncle ( Fig. 10 A, B) reaching midlength of antennal scale. First segment subequal in length to distal two segments combined, dorsodistal margin armed with 1 strong tooth directed forward in dorsal view and obliquely erect in lateral view; stylocerite elongate, faintly sinuous, reaching distal end of antennular peduncle, bearing small, low protuberance proximolaterally. Second segment about 0.6 length of first segment, armed with l strong dorsolateral distal tooth. Third segment short, armed with 1 strong dorsodistal tooth. Upper flagellum with thickened aesthetasc-bearing portion about 0.3 of carapace length; lower flagellum longer than upper flagellum, articles each with few short setae on distal margin.

Antenna ( Figs. 10 A, B, 12C) with basicerite bearing strong ventrolateral distal tooth directed slightly laterally; dorsolateral distal angle also produced into strong tooth slightly shorter than ventrolateral distal tooth. Carpocerite falling slightly short of midlength of antennal scale. Antennal scale 0.8 times as long as carapace and 2.2 times longer than wide; lateral margin nearly straight or faintly convex in proximal half; dorsal surface with blunt median ridge; distolateral tooth not reaching broadly rounded distal margin of lamella, supported by longitudinal keel extending to base of antennal scale. Flagellum slightly shorter than body.

Mouthparts without distinctive features.

Third maxilliped ( Fig. 11 A) stout, overreaching distal margin of antennal scale by 0.2 length of ultimate segment. Ultimate segment 2.7 times as long as penultimate segment (= carpus), somewhat depressed dorsoventrally, tapering to rounded distal end only in distal 0.2; dorsal, lateral and ventral surfaces with numerous tufts of short setae; mesial surface with numerous transverse tracts of stiff setae, also forming grooming apparatus; distal part circumscribed by small, darkly pigmented spines ( Fig.12 D). Carpus short, with tufts of short transverse rows of stiff setae on dorsal and lateral surfaces; mesial surface with numerous transverse tracts of stiff setae, forming grooming apparatus. Antepenultimate segment strongly depressed in proximal half, distal part subtrigonal in cross section; lateral surface bluntly ridged longitudinally, with row of spiniform setae over entire length; distal margin with small tooth dorsally and strong tooth laterally, and with row of spiniform setae on either side of dorsodistal tooth and around base of distolateral tooth ( Fig. 12 E).

Strap-like, terminally hooked epipods present on third maxilliped to third pereopod, corresponding setobranchs present on first to fourth pereopods.

First pereopod ( Fig. 11 B) stout, reaching distal 0.2 of antennal scale by tip of fingers. Dactylus about 0.6 times as long as palm, terminating in 2 darkly pigmented corneous claws ( Fig. 12 H); fixed finger terminating in single corneous claw ( Fig. 12 H); both fingers each with 1 darkly pigmented, flattened spines proximal to base of terminal claw(s) on either side ( Fig. 12 I). Palm subcylindrical, about twice as long as wide. Carpus widened distally, cuplike, slightly shorter than palm, distomesial margin with deep notch; grooming apparatus consisting of short, obliquely longitudinal row of setae on ventromesial surface of palm and several short transverse rows of setae on mesial surface of carpus ( Fig. 12 G). Merus slightly narrowing proximally, with small tubercle proximodorsally and with several sets of minute spiniform setae on proximal half of ventral margin ( Fig. 12 J). Ischium with blunt ventrodistal angle.

Second pereopod ( Fig. 11 C) slender, overreaching antennal scale by about 0.3 length of carpus. Carpus divided into 7 articles, third article longest.

Third to fifth pereopods relatively stout, similar in shape but slightly decreasing in length toward posterior. Third pereopod ( Fig. 11 D) overreaching antennal scale by 0.3 length of propodus; dactylus ( Fig. 12 K) 0.25–0.3 times as long as propodus, stout (about 3.5 times as long as wide), terminating in darkly pigmented unguis, armed with 4–6 darkly pigmented accessory spines on flexor margin, these accessory spines increasing in size distally, distalmost spinule subconical, making tip of dactylus biunguiculate; propodus with numerous darkly pigmented spinules, arranged in irregular 3 or 4 rows, on flexor surface; carpus slightly less than half length of propodus, slightly widened distally, unarmed; merus armed with lateroventral row of 9–11 spines on over entire length, but without additional smaller spines not aligned with lateroventral row; ischium occasionally with tiny spine on lateral surface. Fourth pereopod ( Fig. 11 E) reaching distal margin of antennal scale by tip of dactylus; merus with lateroventral row of 7–10 spines, but without additional spines. Fifth pereopod ( Fig. 11 F) not reaching distal margin of antennal scale; propodus with brush-like grooming setae distally ( Fig. 12 L); merus armed with lateroventral row of 6 or 7 spines, but without additional spines; ischium always unarmed.

Protopods of pleopods each with deep ventrolateral lamina distally terminating in subacute or blunt point.

Uropod ( Fig. 10 E) with protopod bearing sharp posterodorsal tooth, posterolateral angle terminating in strong tooth. Exopod with small spine just mesial to tiny posterolateral tooth; dorsal surface with distinct longitudinal carina lateral to midline. Endopod with distinct median carina and scattered setae on dorsal surface laterally.

Eggs 3.7 x 2.7 mm, not counted.

Males. Generally similar to females except for sexual characters and smaller body size. Rostrum ( Fig. 13 A) about 0.8 times as long as carapace, with 1 or 2 dorsal and 3 or 4 ventral teeth. Carapace ( Fig. 13 A) with 4 postrostral teeth. Ventral teeth of first to fifth pleura ( Fig. 13 B) stronger than in females; fourth pleuron with 1 or 2 ventral teeth in addition to strong posteroventral tooth. Outer antennular flagellum ( Fig. 13 A) with thickened aesthetasc-bearing portion about 0.5 length of carapace; inner flagellum ( Fig. 13 A) elongate and stout, not tapering distally, 1.3–1.9 times as long as carapace; majority of articles wider than long, each article with 1 or 2 minute setae on ventrodistal margin. Endopod of first pleopod ( Fig. 13 C) rather abruptly tapering distally to terminal appendix interna in distal 0.3; mesial margin fringed with short simple setae becoming longer and widely spaced distally; lateral margin sinuous, with row of moderately long plumose setae extending to distal 0.3. Second pleopod with appendix masculina ( Fig. 13 D) 0.7 length of appendix interna, as stout as appendix interna, rounded terminally, bearing numerous stiff setae on distal end to distal 0.6 of mesial surface.

Coloration in life. Unavailable.

Size. Largest male cl 17.3 mm, largest female cl 25.4 mm, ovigerous female cl 23.5 mm.

Variation. The rostrum bears one dorsal tooth (four specimens) except for the male paratype (CBM-ZC 12599), in which there are two dorsal teeth. The number of the postrostral teeth on the carapace is variable, four in the male specimens or five in the female specimens, although it could not be concluded if this variation is sexrelated. Ventral teeth on pleura of the pleon seem to become smaller with increase of the animal size in females. The number of ventral teeth of the fifth pleomere is variable from two to four (mostly three) on one side, but none of the specimens examined has two ventral teeth on both sides. Like other congeneric species (cf. Komai et al. 2004, 2012; Komai 2013), the new species exhibits strong sexual dimorphism in the structure of the inner antennular flagellum (see above description; cf. Figs. 10 A and 13A).

Distribution. Known only from Kitami-Yamato Bank, southwestern Sea of Okhotsk, at depth of 156– 208 m.

Remarks. As mentioned above, Lebbeus magnificus n. sp. is morphologically closer to L. groenlandicus than to L. armatus . Nevertheless, the new species is readily distinguished from L. groenlandicus by the following characters (see Table 2 ): the dorsal margin of the rostrum is armed usually with only one tooth in L. magnificus n. sp., rather than two to four teeth in L. groenlandicus ; the postrostral teeth on the carapace in the female is five in L. magnificus n. sp., rather than four in L. groenlandicus ; ventral teeth on pleura of the pleon are generally weaker in L. magnificus n. sp. than in L. groenlandicus ; the fifth pleuron is armed usually with three or four teeth in L. magnificus n. sp., instead of two teeth in L. groenlandicus ; the inner antennular flagellum of males is thicker in L. magnificus n. sp. than in L. groenlandicus ; meral spines on the third to fifth pereopods are more numerous in L. magnificus n. sp. than in L. groenlandicus (for detail, see Table 2 ).

Etymology. The specific epithet “ magnificus ” refers to the beautiful appearance of the new species.

Figures

FIGURE 9. Lebbeus magnificus n. sp., holotype, ovigerous female (cl 24.0 mm), Kitami Yamato Bank, southwestern Sea of Okhotsk, CBM-ZC 12597, entire animal in lateral view. Scale bar: 10 mm.

FIGURE 10. Lebbeus magnificus n. sp., holotype, ovigerous female (cl 24.0 mm), Kitami Yamato Bank, southwestern Sea of Okhotsk, CBM-ZC 12597. A, anterior part of carapace and cephalic appendages, right lateral view (setae partially omitted); B, same, dorsal view (marginal setae on antennal scales omitted; right stylocerite damaged); C, tergite of second pleomere, lateral view; D, third to sixth pleomeres, lateral view; E, posterior part of sixth pleomere, telson, and left uropod, dorsal view (marginal setae on uropodal rami omitted); F, posterior margin of telson, dorsal view (right spines broken off). Scale bars: 5 mm for A – E; 1 mm for F.

FIGURE 11. Lebbeus magnificus n. sp., holotype, ovigerous female (cl 24.0 mm), Kitami Yamato Bank, southwestern Sea of Okhotsk, CBM-ZC 12597. Thoracic appendages, lateral view. A, right third maxilliped; B, right first pereopod; C, left second pereopod; D, right third pereopod; E, right fourth pereopod; F, right fifth pereopod. Scale bar: 5 mm.

FIGURE 12. Lebbeus magnificus n. sp., holotype, ovigerous female (cl 24.0 mm), Kitami Yamato Bank, southwestern Sea of Okhotsk, CBM-ZC 12597. A, suborbital lobe of carapace, dorsolateral view; B, posterior part of sixth pleomere and anterior part of telson, lateral view; C, right antenna, ventral view (marginal setae on antennal scale omitted); D, right third maxilliped, distal part of ultimate segment, dorsal view; E, same, distal part of antepenultimate segment, lateral view; F, right first pereopod, chela, extensor view; G, same, chela and carpus, mesial view; H, I, same, tip of fingers; J, same, ventral margin of proximal part of merus and distal part of ischium, mesial view; K, right third pereopod, dactylus, lateral view; L, right fifth pereopod, dactylus, lateral view. Scale bars: 5 mm for A – C, G; 2 mm for D – F, J, K, L; 1 mm for H, I.

FIGURE 13. Lebbeus magnificus n. sp., paratype, male (cl 17.7 mm), Kitami Yamato Bank, southwestern Sea of Okhotsk, CBM-ZC 12598. A, carapace and cephalic appendages, left lateral view; B, pleon, left lateral view; C, endopod of left first pleopod, ventral view; D, appendices interna and masculina of left second pleopod, mesial view. Scale bars: 5 mm for A, B; 1 mm for C, D.