Metacrangon sinensis Fujino & Miyake, 1970

Komai, Tomoyuki, 2012, 3468, Zootaxa 3468, pp. 1-77 : 56-59

Metacrangon sinensis Fujino & Miyake, 1970

( Figs 29, 30, 41)

Metacrangon sinensis Fujino & Miyake, 1970: 269 , figs. 10–15; Kim & Park 1972: 208; Kim 1976: 146; 1977: 315, pl. 33, fig. 68, text-fig. 142; Miyake 1982: 189 (list); Liu & Zhong 1994: 561 (list); Komai 1994: 97 (list); Cha et al. 2001: 152, 153, unnumbered figs; Li 2008: 723 (list); De Grave & Fransen 2011: 458 (list).

Material examined. Non-type : northern part of East China Sea, 37°30.0’N, 123°14.3’E, 68 m, 29 January 1965, 11 males (cl 3.9–5.1 mm), 11 females (cl 5.2–7.4 mm), 2 ovigerous females (cl 7.0, 7.3 mm), 1 juvenile (cl 3.0 mm), ZLKU 14312 ; similar locality, 37°30.0’N, 123°14.3’E, 68 m, 29 February 1965, 1 female (cl 6.0 mm), ZLKU 14344 ; similar locality, 37°27.7’N, 124°27.6’E, 75 m, 5 males (cl 4.0– 5.7 mm), 6 ovigerous females (cl 7.2–9.4 mm), ZLKU 14408 ; similar locality, 37°23.7’N, 123°16.9’E, 67 m, 8 November 1966, 6 females (cl 5.5–9.2 mm), 7 ovigerous females (cl 7.2–8.7 mm), ZLKU 14461 .

Type material. Holotype: northern part of East China Sea, 37°01.5’N, 123°57.9’E, 74 m, 9 November 1966, ovigerous female, ZLKU 14533 . Not examined.

Paratypes: 37°00.0’N, 124°15.0’E, 76 m, 9 November 1966, 4 females (cl 4.0– 6.7 mm), 4 ovigerous females (cl 7.6–9.7 mm), ZLKU 14513 . Not examined .

Redescription. Female. Rostrum ( Figs 29A, B, G, 30A) directed forward, subtrapezoidal with rounded or subtruncate distal margin in dorsal view, reaching or slightly overreaching antennal teeth (less than 0.2 times as long as carapace); dorsal surface faintly sulcate medially; ventral carina high. Carapace ( Figs 29A, B, E, 30A) widened posteriorly and wider than long postorbitally in spawning molt; middorsal carina sharp, extending nearly to posterodorsal margin of carapace, with 2 relatively small, laterally compressed teeth; anterior tooth directed forward, compressed laterally, epigastric in position (arising between anterior 0.1 and 0.2 of carapace length); posterior tooth subequal in size to or slightly larger than anterior tooth, acute or subacute, arising at 0.6–0.7 of carapace length; submedian teeth present; antennal tooth directed forward in lateral view, subacute, supported by sharp carina with noticeably convex lateral margin; branchiostegal tooth moderately strong, directed forward in dorsal view, ascending in lateral view (angle about 30° against horizontal plane of carapace), reaching or slightly overreaching dorsolateral distal angle of basicerite; postorbital angle rounded; orbital cleft present; anterolateral margin between antennal tooth and branchiostegal tooth slightly sinuous, unarmed; branchiostegal carina reaching to level of posterior end of hepatic groove; branchial carina absent.

Abdomen ( Fig. 29C–E) slightly sculptured. First to fifth abdominal somites with narrow, distinct middorsal carina, none reaching posterodorsal margin of respective somite. First to third abdominal pleura rounded marginally, posteroventral angle of fourth pleuron rounded. Sixth abdominal somite with distinct, straight submedian carinae; dorsolateral surface distinctly depressed. Telson ( Fig. 29E) with 2 pairs of dorsolateral spines, first pair located at midlength.

Eye ( Fig. 29G) about as long as wide; cornea as wide as eyestalk, its width slightly less than 0.2 of carapace length; eyestalk with dorsodistal protrusion far falling short of distal corneal margin, bearing rounded dorsal tubercle.

Antennular peduncle ( Figs 29G, 30A) relatively stout, reaching midlength of antennal scale. First segment with short, blunt distolateral process; stylocerite broad, abruptly tapering to small blunt or subacute tooth, falling short of distolateral process of first segment, lateral margin obtusely angular proximally. Second segment with short, blunt distolateral process. Outer flagellum short, reaching or slightly overreaching distal margin of lamella of antennal scale, consisting of 9–11 articles.

Antenna ( Fig. 29G, 30A) with basicerite having dorsolateral distal angle only slightly produced, rounded, ventrodistal tooth flattened dorsoventrally, subacute or blunt. Antennal scale about 0.5 times as long as carapace, 1.5– 1.6 times longer than wide; lateral margin slightly convex; distolateral tooth broad, very short, falling short of distal margin of lamella; lamella weakly produced, broadly rounded.

Third maxilliped stout, ultimate segment 3.3–3.4 times longer than wide, penultimate segment about 1.8 times longer than wide ( Fig. 30B).

First pereopod ( Fig. 30C, D) with palm 2.5–2.8 times longer than wide, slightly narrowing distally, lateral and mesial margins slightly sinuous; carpus with distolateral tooth; merus with 1 small dorsodistal spine, ventral margin strongly sinuous, crested. Second and third pereopods typical of genus (not illustrated); third pereopod reaching or slightly overreaching distal margin of antennal scale. Fourth pereopod ( Fig. 30E) stout, reaching or slightly overreaching distal margin of antennal scale; dactylus ( Fig. 30F) spatulate with proximally convex dorsal and nearly straight ventral margins, 3.3–3.5 times longer than wide. Fifth pereopod ( Fig. 30G) with dactylus subspatulate, 0.8 times as long as propodus, slightly longer than that of fourth pereopod ( Fig. 30H); merus-ischium combined about 0.7 times as long as that of fourth pereopod.

Uropodal exopod with blunt or subacute posterolateral tooth; no spinule mesial to posterolateral tooth ( Fig. 30I).

Eggs 1.4 x 1.3 mm; not counted.

Male. Carapace slightly longer than or as long as wide postorbitally. Cornea ( Fig. 30J) 0.2 or slightly more of carapace length. Outer antennular flagellum ( Fig. 30J) overreaching antennal scale by half-length, consisting of 15–17 articles (articles much wider than long except for first article).

Size. Largest male 7.4 mm; largest female cl 9.4 mm, ovigerous females cl 7.0– 9.4 mm.

Coloration. According to the color photograph given by Cha et al. (2001): carapace and posterior part of fourth abdominal somite, fifth and sixth somites dark brown, and posterior part of branchial region of carapace, first to anterior part of fourth abdominal somites and tail fan milky white. Antennae, third maxilliped, first to fourth pereopods brown, fifth pereopod whitish.

Distribution. Known only from the northern part of the East China Sea and the southern part of Korea ( Fig. 41); 59– 150 m.

Remarks. Metacrangon sinensis was originally described from the northern part of the East China Sea at depths of 59–150 m, being most abundant in the entrance to Liaotung Bay ( Fujino & Miyake 1970). Since the original description, it has been reported from Korean waters only ( Kim 1976, 1977; Cha et al. 2001), suggesting a very narrow geographical range. In this study, some lots from the material studied by Fujino & Miyake (1970) were examined, although the holotype and paratypes were not examined. The original description is sufficient for species recognition, but an updated description is given to present diagnostic details not mentioned in the original description.

This species somewhat resembles M. asiaticus , M. proxima and M. variablis in the position of teeth on the carapace and the presence of a middorsal carina on the second to fifth abdominal somites. Metacrangon sinensis is readily distinguished from these three species by the trapezoidal rostrum with a convex to roundly truncate distal margin, the sharply carinate lateral margin of the antennal tooth on the carapace and the different shape of the antennal scale. In M. asiaticus , M. proxima and M. variablis , the rostrum is triangular with an acute to subacute apex; and the antennal tooth is not carinate on the lateral margin. The antennal scale of M. sinensis is relatively broad (1.5–1.6 times longer than wide); the lateral margin is straight or slightly convex, terminating in a broad, small distolateral tooth; the distal lamella is broadly rounded. In contrast, the antennal scale of the latter five species is more than 2.0 times longer than wide; the lateral margin is concave, terminating in a strong distolateral tooth; the distal lamella is distinctly narrower or more strongly produced.