Metacrangon obliqua, Komai, 2012

Komai, Tomoyuki, 2012, 3468, Zootaxa 3468, pp. 1-77 : 47-50

Metacrangon obliqua n. sp.

( Figs 24, 25, 41)

Type material. Holotype: NW of Matsumae-ko-jima Islet , southern Hokkaido, Sea of Japan, 250–300 m, 9 June 1991, shrimp trap, coll. Igarashi, 1 ovigerous female (cl 12.4 mm), CBM-ZC 10673.

Description. Female (holotype). Rostrum ( Figs 24A, B, G, 25A) triangular in dorsal view, somewhat ascending (angle against horizontal plane of carapace about 30°), overreaching antennal teeth (slightly less than 0.2 times as long as carapace); tip blunt in dorsal view; dorsal surface shallowly concave; ventral carina high. Carapace ( Figs 24A, B, G, 25A) widened posteriorly, nearly as long as wide postorbitally; middorsal carina extending to posterior 0.2 of carapace, with 2 greatly unequal middorsal teeth; anterior tooth epigastric in position (arising at about 0.1 of carapace length), slender, subconical, obliquely erect, not reaching base of rostrum, tip subacute; posterior tooth much smaller than anterior tooth, arising at about 0.6 of carapace length; no denticle present between 2 middorsal teeth; submedian teeth present; antennal tooth ascending in similar degree to rostrum in lateral view, acute; postorbital angle rounded (left) or slightly produced (right); orbital cleft present; anterolateral margin between antennal and branchiostegal teeth sinuous, with tiny denticle; branchiostegal tooth moderately strong, directed forward in dorsal view, ascending in similar degree to rostrum in lateral view, slightly overreaching distolateral angle of antennal basicerite; branchiostegal carina curving, not reaching level of posterior end of hepatic groove; branchial carina absent.

Abdomen ( Fig. 24C–F) slightly sculptured. First and second somites rounded dorsally, posterodorsal margins not elevated; third to fifth somites with low, rather broad, distinct middorsal carinae, those of third and fourth somites not reaching posterodorsal margin of respective somite, that of fifth carina confluent with low, broad anterior transverse carina. Fifth somite with low lateral ridge. Pleura of anterior three somites rounded, anteroventral margin of fourth pleuron rounded. Sixth somite with distinct submedian carinae, reaching nearly to posterodorsal margin; pleuron shallowly depressed; posterodorsal margin broken; posterolateral process terminating in blunt tooth. Telson ( Fig. 24E) at least with 2 pairs of dorsolateral spines, but tip broken off.

Eye ( Fig. 24G) stout, about 1.2 times longer than wide; cornea as wide as eyestalk, its width slightly more than 0.1 of carapace length; eyestalk bearing rounded dorsal tubercle on dorsodistal protrusion not reaching distal corneal margin.

Antennular peduncle ( Figs 24G, 25A) moderately stout, distinctly overreaching midlength of antennal scale. First segment with prominent, acuminate distolateral process directed forward and reaching midlength of second segment; stylocerite terminating in slender, acute tooth, far falling short of distolateral process of first segment, lateral margin obtusely angular. Second segment with prominent, acute, laterally directed distolateral process overreaching distal margin of third segment. Outer flagellum overreaching distal margin of lamella of antennal scale by 0.5 length, consisting of 11 articles.

Antenna ( Figs 24G, 25A) with basicerite having dorsolateral distal angle produced in small subacute tooth, ventrolateral tooth slender, acute. Antennal scale ( Fig. 25B) 0.5 times as long as carapace and about 2.7 times longer than wide; lateral margin concave; distolateral tooth broken off, but estimated reconstruction suggesting relatively slender tooth distinctly overreaching distal margin of roundly triangular lamella.

Third maxilliped ( Fig. 25C) moderately stout; ultimate segment gradually tapering distally in distal half, about 4.5 times longer than wide; penultimate segment about 2.0 times longer than wide.

First pereopod ( Fig. 25D, E) with palm 3.1 times longer than wide, not markedly widened proximally or distally, lateral and mesial margins faintly sinuous; carpus without distolateral tooth; merus with 2 small dorsodistal teeth, ventral margin sinuous, carinate. Second and third pereopods typical of genus ( Fig. 25F, G); third pereopod overreaching distal margin of antennal scale by length of dactylus. Fourth pereopod ( Fig. 25H) moderately stout; dactylus ( Fig. 25I) spatulate, subtriangular with slightly convex dorsal and nearly straight ventral margins, 3.9 times longer than broad. Fifth pereopod ( Fig. 25J) with dactylus subspatulate, about 0.8 times as long as propodus ( Fig. 25K); merus-ischium combined about 0.8 times as long as that of fourth pereopod.

Uropodal exopod with laterally pointed posterolateral tooth; spinule present mesial to posterolateral tooth ( Fig. 25L).

Eggs 2.0 x 1.6 mm; not counted.

Males unknown.

Coloration. Unknown.

Size. Ovigerous female cl 12.4 mm.

Distribution. Known only from the type locality, Sea of Japan off Matsumae, southern Hokkaido ( Fig. 42); 250– 300 m.

Remarks. This new species is similar to Metacrangon cornuta in the position of carapace teeth, the armature of the antennular peduncle and the shape of the antennal scale. However, it differs from M. cornuta in the shorter rostrum with a rounded tip (slightly less than 0.2 times as long as the carapace versus more than 0.3 times as long; the rostral tip is acuminate in M. cornuta ), smaller and more posteriorly arising anterior middorsal tooth on the carapace (at 0.1 of the carapace length versus 0.2), the more clearly delimited middorsal carina on the fourth and fifth abdominal somites and the more stout ultimate segment of the third maxilliped (4.5 times as long as wide versus 6.0 times as long). Metacrangon obliqua n. sp. also closely resembles M. spinirostris . Nevertheless, the not so ascending rostrum, antennal and branchiostegal teeth and non-elongate anterior middorsal tooth on the carapace distinguish the new species from M. spinirostris . In addition, the branchiostegal teeth are directed forward in M. obliqua , rather than distinctly curved laterally as in M. spinirostris .

Etymology. From the Latin obliquus (= oblique), in reference to the prominent, obliquely erected distolateral tooth of the first segment of the antennular peduncle.