Metacrangon longirostris ( Yokoya, 1933 )

Komai, Tomoyuki, 2012, 3468, Zootaxa 3468, pp. 1-77 : 42-46

Metacrangon longirostris ( Yokoya, 1933)

( Figs 21–23, 40)

Crangon longirostris Yokoya, 1933: 36 , text-fig. 17 [type-locality: east of Owase, Mie Prefecture, Japan, 329 m]. Metacrangon longirostris .— Zarenkov 1965: 1764 (list); Miyake 1982: 189 (list); Hayashi 1986: 142, 143, fig. 93; Sakaji 2001:

210; De Grave & Fransen 2011: 457 (list).

Material examined. Japan. Off Shionomisaki, Kii Peninsula, Kumano Sea, 350 m, 21 January 1990, dredge, coll. S. Nagai, 1 male (cl 4.8 mm), 2 females (cl 4.9, 7.7 mm), CBM-ZC 1200 ; same locality, 450 m, 10 December 1990, dredge, coll. S. Nagai, 1 female (cl 9.2 mm), 2 juvenile (cl 4.0, 4.1 mm), CBM-ZC 1201 ; same locality, 2 females (cl 7.0, 7.7 mm), CBM-ZC 3822 ; same locality, 300–350 m, 16 August 1990, dredge, coll. S. Nagai, 1 female (cl 8.4 mm), CBM-ZC 3824 ; same locality, 420 m, 15 February 1992, dredge, coll. S. Nagai, 2 females (cl 5.6, 7.7 mm), CBM-ZC 3825 ; same locality, 300 m, October 1996, dredge, coll. S. Nagai, 1 female (cl 6.9 mm), CBM-ZC 3560 ; same locality, 300 m, 31 March 1996, dredge, coll. S. Nagai, 11 males (cl 3.8–5.2 mm), 11 females (cl 4.8– 8.0 mm), CBM-ZC 9535; Tosa Bay , depth not recorded, 20 November 1958, commercial trawler, coll. Kurohara, 2 females (cl 8.0, 8.5 mm), 3 ovigerous females (cl 9.3–10.7 mm), ZLKU 1498–1503 ; Tosa Bay , 400 m, 25 October 1988, trawl ( RV Kotaka-maru), coll. M. Toriyama, 1 female (cl 8.6 mm), CBM-ZC 10671; off Cape Ashizuri, Tosa Bay, 350 m, 10 March 1988, commercial trawler, 8 females (cl 9.0– 10.7 mm) (MNHN-Na) .

Type material. Syntypes. RV Soyo-maru : stn 381, east of Owase, Kumano-nada, 34°03.45’N, 136°32.45’E, 329 m, 3 December 1927, beam trawl, 1 male, 2 ovigerous females (size not specifically indicated). Presumed no longer extant .

Redescription. Female. Rostrum ( Figs 21A, B, E, 22A) narrowly triangular in dorsal view, slightly ascending or directed forward, overreaching antennal teeth by half length (about 0.2–0.3 times as long as carapace); tip bluntly pointed in dorsal view; dorsal surface with faint grooves along lateral margins; ventral carina high. Carapace ( Fig. 21A, B, E, 22A) widened posteriorly in spawning molt, longer than wide postorbitally; middorsal carina extending to posterior 0.2 of carapace, with 2 unequal, acute middorsal teeth; anterior tooth arising slightly posterior to rostral base, compressed laterally, obliquely erect, reaching or slightly falling short of rostral base; posterior tooth smaller than anterior tooth, arising at about 0.6 of carapace length; no denticle between two middorsal teeth; submedian teeth present; antennal tooth somewhat ascending in lateral view (angle against horizontal plane of carapace 30–50°), elongate, acute or subacute; postorbital angle produced into prominent tooth nearly reaching to level of tip of antennal tooth; anterolateral margin between antennal and branchiostegal teeth usually with tiny acute denticle; branchiostegal tooth moderately strong, directed forward in dorsal view, ascending in similar degree to antennal tooth in lateral view, compressed dorsoventrally, reaching dorsolateral distal angle of antennal basicerite; branchiostegal carina not reaching level of hepatic tooth; branchial carina absent.

Abdomen ( Fig. 21C, D) slightly sculptured; first and second somites rounded dorsally, posterodorsal margins not elevated; third to fifth somites with low, distinct middorsal carina, none reaching posterodorsal margin of respective somite, that of fifth carina confluent with low, broad anterior transverse carina. Third and fourth somites each with obsolete lateral ridge; fifth somite also with 2 obsolete lateral ridges. Pleura of anterior three somites rounded; anteroventral angle of fourth pleuron rounded. Sixth somite with distinct submedian carinae, not reaching posterodorsal margin; posterodorsal margin bilobed; posterolateral process terminating in sharp tooth. Telson ( Fig. 21C) with 2 pairs of dorsolateral spines, first pair located slightly posterior to midlength.

Eye ( Figs 21E, 22B) moderately stout, 1.2–1.3 times longer than wide; cornea not wider than eyestalk, its width about slightly less than 0.2 of carapace length; eyestalk with dorsodistal protrusion not reaching distal corneal margin in dorsal view, bearing rounded dorsal tubercle.

Antennular peduncle ( Figs 21E, 22A) moderately stout, reaching distal 0.2–0.3 of antennal scale. First segment with short, blunt distolateral process directed anteriorly; stylocerite terminating in elongate projection slightly curved mesially and reaching to tip of distolateral process of first segment, lateral margin gently convex. Second segment widened distally, with short, blunt, laterally directed distolateral process. Outer flagellum overreaching distal margin of lamella of antennal scale by 0.5–0.6 length, consisting of 9–13 articles.

Antenna ( Figs 21E, 22A) with basicerite having dorsolateral distal angle produced in small triangular process, ventrolateral tooth acute. Antennal scale 0.4–0.5 times as long as carapace and about 3.0 times longer than wide; lateral margin concave; distolateral tooth narrow, falling short of distal margin of lamella; lamella strongly produced, roundly triangular.

Third maxilliped ( Fig. 22C) relatively slender; ultimate segment gradually tapering distally, about 7.5 times longer than wide; penultimate segment about 3.2 times longer than wide.

First pereopod ( Fig. 22D, E) with palm about 3.4 times longer than wide, not markedly widened proximally or distally, lateral and mesial margins nearly straight; carpus without distolateral tooth; merus with 1 small dorsodistal tooth, distolateral margin unarmed, ventral margin slightly sinuous, carinate. Second and third pereopods typical of genus ( Fig. 22F, G); third pereopod reaching or slightly overreaching distal margin of antennal scale. Fourth pereopod ( Fig. 22H) moderately stout, overreaching distal margin of antennal scale by half length of dactylus; dactylus ( Fig. 22I) spatulate with distinctly convex dorsal and very slightly convex ventral margins, 5.0–5.5 times longer than wide. Fifth pereopod ( Fig. 22J) with dactylus subspatulate, slightly curved, 0.8–0.9 times as long as propodus, slightly shorter than that of fourth pereopod ( Fig. 22K).

Uropodal exopod with posterolateral tooth blunt or subacute; no spinule mesial to posterolateral tooth ( Fig. 22L).

Male. Carapace ( Fig. 23A, B) with middorsal and antennal teeth and postorbital process more strongly produced than in females, anterior middorsal tooth reaching to rostral base; cornea large, its width more than 0.2 of carapace length; outer antennular flagellum ( Fig. 23A) longer than peduncle, consisting of 10–13 articles (articles as wide as or slightly wider than long except for first article).

Coloration. Carapace and posterior half of abdomen reddish brown with scattered white spots, anterior part of abdomen white with reticulate pattern of pale reddish brown on tergites. Telson and uropods generally white, telson with tinge of reddish brown. Cornea gray.

Size. Largest female cl 10.7 mm, ovigerous females cl 9.3–10.7 mm, largest male cl 5.2 mm.

Distribution. Restricted to the Pacific coast of Honshu, Japan, from Kumano Sea to Tosa Bay ( Fig. 40); 300– 450 m.

Remarks. The type series consists of three specimens (including one male and two ovigerous females), but Yokoya (1933) did not designate a holotype. Therefore, the three specimens are syntypes. It was not possible to locate these syntypes during this study, and they are presumed to be no longer extant. The present material contains specimens from the Kumano Sea off Shionomisaki, close to the type locality.

Metacrangon longirostris is unique within the genus in having a postorbital angle produced in a prominent, spiniform process.