Metacrangon asiaticus ( Kobjakova, 1955 )

Komai, Tomoyuki, 2012, 3468, Zootaxa 3468, pp. 1-77 : 63-68

Metacrangon asiaticus ( Kobjakova, 1955)

( Figs 33–36, 42)

Sclerocrangon variabilis asiaticus Kobjakova, 1955: 236 , fig. 2.

Metacrangon variabilis . — Birshtein & Zarenkov 1970: 441.

Metacrangon variabilis asiaticus . — De Grave & Fransen 2011: 458 (list).

Material examined. Kuril Islands. RV Tanshu-maru , research cruise to South Kuril Islands in 1992, stn BB08 , E of Iturup Island , 28 April 1992, otter trawl, 1 female (cl 9.0 mm), CBM-ZC 9541; stn BB31 , NE of Iturup Island , 45°14’N, 149°15’E, 625–642 m, sand, 3 May 1992, otter trawl, 5 females (cl 8.3–10.1 mm), CBM-ZC 9542; stn BB35 , similar locality, 45°17’N, 150°14’E, 614–620 m, sand, 5 May 1992, otter trawl, 1 male (cl 7.4 mm), 1 ovigerous female (cl 10.8 mm), CBM-ZC 9543; stn BVD4, SE of Iturup Island , 43°29’N, 147°01’E, 410–414 m, 7 May 1992, otter trawl, 1 male (cl 5.5 mm), 2 females (cl 7.7, 10.0 mm), CBM-ZC 9544 .

Type material. Syntypes: 4 females (cl 9.0–11.0 mm), 2 males (cl 9.0, 9.8 mm), off Iturup Island , South Kuril Islands ; illustrated specimen (size not indicated), SE of Shikotan Island , South Kuril Islands. Probably deposited in the Zoological Institute, St. Petersburg. Not examined .

Redescription. Female. Rostrum ( Figs 33A–C, 35A) triangular in dorsal view, directed forward to somewhat ascending (angle against horizontal plane of carapace about 30° at most), slightly overreaching antennal teeth (slightly less than 0.2 times as long as carapace); tip in dorsal view blunt or subacute; dorsal surface nearly flat; ventral carina high. Carapace ( Figs 33A, B, 35A) widened posteriorly in spawning molt, slightly longer than wide postorbitally; middorsal carina extending to posterior 0.20 of carapace, with two unequal middorsal teeth; anterior tooth epigastric in position (arising between anterior 0.1 and 0.2 of carapace length), slender, subconical, obliquely erect, not reaching base of rostrum, tip acute or blunt; posterior tooth much smaller than anterior tooth, arising at 0.6 of carapace length; minute denticle between two middorsal teeth sometimes present; submedian tooth present; antennal tooth directed forward in lateral view, acuminate; branchiostegal tooth moderately strong, directed forward in dorsal view, ascending in similar degree to rostrum in lateral view, slightly overreaching dorsodistal lateral angle of antennal basicerite; postorbital angle produced in small, triangular lobe; orbital cleft present; anterolateral margin between antennal and branchiostegal teeth usually with minute acute denticle inferior to antennal tooth; branchiostegal carina curving in lateral view, not reaching level of hepatic tooth; branchial carina absent.

Abdomen ( Fig. 33D, E) slightly sculptured; first and second somites rounded dorsally or with trace of middorsal carina; third to fifth somites with low, rather broad, distinct middorsal carina, carina on third and fourth somites not reaching posterodorsal margins of respective somites, that of fifth carina reaching to posterodorsal margin. Tergites of second to fifth somites not elevated along posterior margin. Third somite with obsolete lateral ridge; fourth and fifth somites with distinct lateral ridge. Pleura of anterior three somites rounded, fourth pleuron with rounded anteroventral angle. Sixth somite with distinct submedian carinae; posterodorsal margin weakly bilobed; posterolateral process terminating in subacute tooth. Telson with 2 pairs of dorsolateral spines, first pair located posterior to midlength.

Eye ( Figs 33C, 35A) moderately stout, 1.5–1.6 times longer than wide; cornea as wide as eyestalk, its width about less than 0.2 of carapace length; eyestalk with dorsodistal protrusion not reaching distal corneal margin, bearing rounded dorsal tubercle.

Antennular peduncle ( Fig. 35A) distinctly overreaching midlength of antennal scale. First segment with short, blunt distolateral process; stylocerite terminating in subacute tooth, far falling short of distolateral process of first segment, lateral margin angular, occasionally produced. Second segment widened distally, with prominent distolateral process. Outer flagellum distinctly shorter than peduncle, overreaching lamella of antennal scale by 0.6–0.7 length, consisting of 9–11 articles.

Antenna ( Fig. 35A) with basicerite having dorsolateral distal angle produced in bluntly pointed lobe, ventrodistal tooth acute. Antennal scale short, about 0.4 times as long as carapace and about 2.4–2.5 times longer than wide; lateral margin concave; distolateral tooth relatively broad, reaching distal margin of lamella; lamella subtriangular with rounded distal margin.

Third maxilliped ( Fig. 35B) moderately stout; ultimate segment gradually tapering distally in distal half, 4.0– 4.5 times longer than wide; penultimate segment about 2.1 times longer than wide.

First pereopod ( Fig. 35C, D) moderately stout; palm about 2.4 times longer than wide, not markedly widened proximally or distally, lateral and mesial margins faintly sinuous; carpus without distolateral tooth; merus with 1 small dorsodistal tooth, ventral margin sinuous, carinate. Second and third pereopods typical of genus ( Fig. 35E– H); third pereopod overreaching antennal scale by length of dactylus and half of propodus. Fourth pereopod ( Fig. 35I) moderately stout, reaching antennal scale by tip of dactylus; dactylus ( Fig. 35J) spatulate with distinctly convex dorsal and faintly convex ventral margins. Fifth pereopod ( Fig. 35K) with dactylus subspatulate, about 0.8 times as long as propodus, shorter than that of fourth pereopod ( Fig. 35L); merus-ischium combined about 0.7 times as long as that of fourth pereopod.

Uropodal exopod with acute posterolateral tooth; no spinule mesial to posterolateral tooth ( Fig. 35M).

Males. Carapace ( Fig. 36A) with middorsal and antennal teeth stronger than in females. Outer antennular flagellum ( Fig. 36B) slightly longer than peduncle, composed of 19 articles (articles as wide as or slightly wider than long except for first article). Appendix masculina bearing numerous stiff simple setae.

Coloration. Not known.

Size. Largest male cl 9.0 mm; largest female cl 10.8 mm, ovigerous female cl 10.8 mm.

Distribution. South Kuril Islands and Komandor Islands ( Fig. 42); 136– 642 m.

Remarks. The present topotypic material agrees well with the original description of Sclerocrangon variabilis asiaticus by Kobjakova (1955), particularly in the shape of the anterior middorsal tooth on the carapace. In addition, the shortness of the antennal scale is clearly illustrated in the original figure.

Kobjakova (1955) illustrated a specimen from off Shikotan Island as an example of the type and provided a summarizing measurements of six specimens from off Iturup Island . She did not specifically designate a holotype, and thus these specimens are considered to be syntypes. She also mentioned the existence of specimens from Komandor Islands in the western Bering Sea , and thus these specimens are also considered to be syntypes. Unfortunately , no access to the type material was available during the present study (supposedly preserved in the Zoological Institute, St. Petersburg), but the present topotypic material enables a redescription of this poorly known species .

This taxon was originally described as a subspecies of Metacrangon variabilis (as Sclerocrangon ). Comparison of the present specimens with the descriptions of M. variabilis (cf. Rathbun 1904; Schmitt 1921; Zarenkov 1960; Kim 2005) has revealed the existence of some minor differences, warranting the recognition of Kobjakova’s (1955) taxon as a distinct species. These differences include: the anterior middorsal tooth on the carapace is larger than the posterior tooth in M. asiaticus , rather than subequal to the latter in M. variabilis ; the antennal scale is relatively shorter in M. asiaticus than in M. variabilis (about 0.4 times as long as the carapace versus about 0.5 times); and the distolateral tooth of the antennal scale is more slender and is separated from the distal lamella by a broader notch in M. asiaticus than in M. variabilis . These two species are also similar to M. proxima and M. tsugaruensis sp. nov. (see the accounts of respective species).

Birshtein & Zarenkov (1970) reported Metacrangon variabilis from the Kuril Islands, although they noted that their material agreed well with Kobjakova’s (1955) description. Consequently, this record is here referred to M. asiaticus .