Metacrangon nipponensis ( Yokoya, 1933 )

Komai, Tomoyuki, 2012, 3468, Zootaxa 3468, pp. 1-77 : 26-30

Metacrangon nipponensis ( Yokoya, 1933)

( Figs 11–13, 40)

Crangon nipponensis Yokoya, 1933: 38 , text-fig. 19 [type-locality: east of Sioya-zaki, 539 m].

Metacrangon nipponensis .— Zarenkov 1965: 1764 (list); Komai 1994: 97 (list); Komai & Komatsu 2009: 520, fig. 19F; De Grave & Fransen 2011: 457 (list).

Mesocrangon nipponensis .— Miyake 1982: 189 (list).

Material examined. Japan. Holotype: RV Soyo-maru , stn 22, E of Shioya-zaki, Fukushima Prefecture, 36°46.40’N, 141°30.00’E, 539 m, 29 June 1926, Kamiya’s dredge, 1 female (cl 8.9 mm), KMNH.

Non-type: RV Tanshu-maru, 1989 cruise, E of Onahama, Fukushima Prefecture, 37°02.4’N, 141°31.4’E, 288 m, 15 November 1989, gut contents of Gadus macrocephalus , coll. O. Yamamura, 1 female (badly damaged), 1 ovigerous female (cl 9.3 mm), CBM-ZC 9536. RV Tanshu-maru, 1994 cruise, stn T-6, Kashima Sea, 16 October 1994, otter trawl, 1 female (cl 7.1 mm), CBM-ZC. RV Tanshu-maru, 1997 cruise, stn F-700, E of Kesen’numa, Miyagi Prefecture, 38°28’N, 142°14’E, 700–762 m, 23 April 1997, otter trawl, coll. K. Uchikawa, 1 male (cl 4.9 mm), CBM-ZC 10668. RV Wakataka-maru, 2005 cruise, stn G450, Kashima Sea, off Onahama, Fukushima Prefecture, 36°51.6’N, 141°28.7’E to 36°52.8’N, 141°30.0’E, 448–454 m, 9 November 2005, trawl, coll. H. Komatsu, 1 female (cl 9.2 mm), NSMT-Cr 16897; stn GH425, Kashima Sea, off Hitachi, Ibaraki Prefecture, 36°39.5’N, 141°17.3’E to 36°40.9’N, 141°18.3’E, 422–425 m, 13 November 2005, 2 females (cl 8.5, 9.2 mm), NSMT-Cr 16895; stn GH480, similar locality, 36°40.8’N, 141°20.8’E to 36°42.3’N, 141°21.6’E, 479–482 m, 13 November 2005, 1 female (cl 8.3 mm), 1 ovigerous female (cl 9.3 mm), NSMT-Cr 16900; 2006 cruise, E480, E of Kinkazan, Miyagi Prefecture, 38°22.7’N, 142°05.2’E to 38°21.2’N, 142°05.9’E, 480–484 m, 3 November 2006, trawl, coll. H. Komatsu, 1 female (cl 8.0 mm), 1 ovigerous female (cl 9.0 mm), NSMT-Cr 17340; stn F425, Kashima Sea, E of Sohma, 37°44.0’N, 141°54.8’E to 37°42.3’N, 141°55.1’E, 424–425 m, 30 October 2006, 1 male (cl 5.3 mm), 1 female (cl 5.0 mm), 1 ovigerous female (cl 9.2 mm), NSMT-Cr; stn FG410 , Kashima Sea, E of Namie, 37°18.8’N, 141°45.8’E to 37°17.1’N, 141°45.5’E, 410 m, 10 November 2006, 1 male (cl 6.6 mm), NSMT-Cr; stn FG450 , similar locality, 37°18.8’N, 141°45.8’E to 37°20.5’N, 141°47.5’E, 444–449 m, 10 November 2006, 1 female (cl 9.4 mm), NSMT-Cr 17334; stn G350, Kashima Sea , E of Onahama, Fukushima Prefecture, 36°56.2’N, 141°30.8’E to 36°57.9’N, 141°31.5’E, 355–373 m, 26 October 2006, 1 ovigerous female (cl 9.1 mm), NSMT-Cr 17335; stn G450, similar locality, 36°51.5’N, 141°28.6’E to 36°52.7’N, 141°30.0’E, 454 m, 27 October 2006, 3 females (cl 8.0– 10.1 mm), 1 ovigerous female (cl 9.1 mm), NSMT-Cr 17335; G480, similar locality, 36°51.2’N, 141°29.2’E to 36°50.0’N, 141°27.7’E, 481–483 m, 27 October 2006, 1 ovigerous female (cl 10.0 mm), NSMT-Cr 17338; stn G510, similar locality, 36°51.4’N, 141°30.1’E to 36°52.1’N, 141°32.1’E, 508 m, 28 October 2006, 1 male (cl 6.0 mm), NSMT-Cr 17339 .

Redescription. Rostrum ( Figs 11, A, B, G, 12A) roundly triangular in dorsal view, somewhat ascending (angle against horizontal plane of carapace about 45°), slightly overreaching antennal teeth (slightly less than 0.2 times as long as carapace); dorsal surface with broad, blunt ridge continuous to middorsal carina on carapace; ventral carina high, ventral margin in lateral view convex, rostral tip in lateral view narrowly rounded. Carapace ( Figs 11A, B, G, 12A) widened posteriorly in spawning molt, slightly longer than wide postorbitally; middorsal carina extending to posterior 0.2 of carapace, with one middorsal tooth arising from slightly posterior to midlength of carapace; no minute denticle between rostral base and middorsal tooth; submedian teeth present; antennal tooth ascending in similar degree to rostrum, subacute; postorbital angle produced in small blunt lobe; anterolateral margin between antennal and branchiostegal teeth usually without denticle; branchiostegal tooth moderately strong, directed forward in dorsal view, ascending in similar degree to rostrum in lateral view, slightly overreaching dorsolateral distal angle of antennal basicerite; branchiostegal carina distinct, curving, reaching level of hepatic tooth; branchial ridge absent.

Abdomen ( Fig. 11C, D, F) barely sculptured. First to third somites rounded dorsally; fourth and fifth somites with only trace of middorsal carina. Fifth somite with 2 blunt ridges laterally. Pleura of anterior three somites rounded, fourth pleuron with rounded anteroventral margin. Sixth somite with distinct submedian carinae; posterodorsal margin slightly bilobed; posterolateral process terminating in acute tooth. Telson ( Fig. 11E) with 2 pairs of sharp dorsolateral spines, first pair located posterior to midlength.

Eye ( Fig. 11G) stout, approximately as long as wide; cornea as wide as eyestalk, its width slightly more than 0.1 of carapace length; eyestalk with dorsodistal protrusion not reaching distal corneal margin, bearing rounded dorsal tubercle.

Antennular peduncle ( Figs 11A, 12A) distinctly overreaching midlength of antennal scale. First segment with distinct, blunt distolateral process; stylocerite far falling short of distolateral process of first segment, terminating in blunt or subacute tooth, lateral margin gently convex to slightly angular. Second segment widened distally, with short, blunt distolateral process. Outer flagellum overreaching lamella of antennal scale by 0.5–0.6 length, consisting of 9–11 articles.

Antenna ( Fig. 11G) with basicerite having dorsolateral distal angle produced in rounded lobe, ventrodistal tooth acute. Carpocerite reaching distal 0.7–0.8 of antennal scale. Antennal scale ( Fig. 11G) 0.4–0.5 times as long as carapace and about 2.7 times longer than wide; lateral margin faintly sinuous or very slightly concave; distolateral tooth moderately broad, distinctly overreaching distal margin of lamella; lamella gently rounded.

Third maxilliped ( Fig. 12B) moderately stout for genus; ultimate segment gradually tapering in distal half, about 5.0 times longer than wide; penultimate segment about 2.0 times longer than wide.

First pereopod ( Fig. 12C, D) moderately stout; palm about 2.8 times longer than wide, not markedly widened proximally or distally, lateral and mesial margins faintly sinuous; carpus with distolateral tooth; merus with 1 small dorsodistal tooth, ventral margin sinuous, carinate. Second and third pereopods typical of genus ( Fig. 12E, F); third pereopod just reaching distal margin of antennal scale by tip of dactylus. Fourth pereopod ( Fig. 12G) stout, slightly falling short of distal margin of antennal scale; dactylus ( Fig. 12H) spatulate with distinctly convex dorsal and faintly convex ventral margins, about 4.8 times longer than broad. Fifth pereopod ( Fig. 12I) with dactylus subspatulate, 0.7 times as long as propodus ( Fig. 12J); merus-ischium combined about 0.8 times as long as that of fourth pereopod.

Uropodal exopod with laterally pointed posterolateral tooth, no spinule mesial to posterolateral tooth ( Fig. 12K).

Eggs 1.7 x 1.4 mm; not counted.

Male. Rostrum ( Fig. 13A, B) more produced than in females, reaching nearly to level of tip of branchiostegal teeth (about 0.2 times as long as carapace); outer flagellum of antennule subequal in length to peduncle, overreaching antennal scale by 0.8 length, consisting of about 10 articles ( Fig. 13B); antennal scale ( Fig. 13B) about 0.6 times as long as carapace.

Coloration in life. Carapace, anterior section of first abdominal somite, and posterior half of second to sixth somites maroon red, posterior section of first somite and anterior part of second somite white with mottled maroon red blotch medially; telson and uropods paler; cornea brownish gray; antenna and pereopods also brown or maroon red ( Komai & Komatsu 2009).

Size. Largest male cl 6.6 mm; largest female cl 10.0 mm, ovigerous females cl 9.0–10.0 mm.

Distribution. Restricted to the Pacific coast of northern Japan from Hokkaido to Kashima Sea ( Fig. 40); 539– 762 m.

Remarks. Metacrangon nipponensis was originally described on the basis of a single female specimen from east of Shioya-zaki, Fukushima Prefecture, at a depth of 539 m (as Crangon ). The holotype is still extant, and now preserved in the collections of KMNH. Recently, Komai & Komatsu (2009) reported additional specimens from off Fukushima Prefecture, although they did not give a detailed account. During the present study, the holotype was reexamined. This species appears most similar to M. monodon from the South Kuril Islands. Differences between the two species are discussed in the account of M. monodon .