Metacrangon tropis, Komai, 2012

Komai, Tomoyuki, 2012, 3468, Zootaxa 3468, pp. 1-77 : 30-34

Metacrangon tropis n. sp.

( Figs 14, 15, 40)

Material examined. Holotype: TRV Shin’yo-maru, 2002 cruise, stn 19, off Izu-oshima Island , Izu Islands, Sagami

Sea , Japan, 35°01.34’N, 139°11.81’E to 35°01.42’N, 139°11.76’E, 173–197 m, 23 October 2002, dredge, coll. T. Komai, ovigerous female (cl 4.7 mm), CBM-ZC 10669 .

Paratype: RV Tansei-maru, KT 04-6 cruise, stn OS-1, off Ohse-zaki , Numazu, Suruga Bay, 35°03.53’N, 138°48.26’E to 35°03.09’N, 138°48.07’E, 135–142 m, 4 May 2004, beam trawl, coll. H. Kohtsuka, 1 female (cl 4.8 mm), CBM-ZC 10670 .

Description. Female. Rostrum ( Figs 14A, B, E, 15A) directed forward, subtrapeziodal with rounded distal margin in dorsal view, arched in lateral view, slightly overreaching antennal teeth (about 0.2 times as long as carapace); ventral carina high, distal end slightly produced beyond rostral tip. Carapace ( Figs 14A, B, E, 15A) not widened posteriorly even in spawning molt, slightly wider than long postorbitally, strongly sculptured with sharp carinae; middorsal carina extending from midlength of rostrum to near posterodorsal margin of carapace, with two teeth and anteriorly diverging branches derived just anterior to base of posterior middorsal tooth; anterior tooth broadly triangular, directed dorsally, strongly compressed laterally, arising at level of rostral base; posterior tooth distinctly smaller than anterior tooth, acuminate, arising at 0.7–0.8 of carapace length; submedian teeth buttressed; hepatic tooth subacute, supported by sharp, strongly sinuous carina extending to branchial region, not connected with branchial carina; antennal tooth directed forward in lateral view, blunt, lateral margin crested with strongly convex outer margin; branchiostegal tooth small, only slightly produced anteriorly, supported by sharp, slightly curving carina extending to level of hepatic tooth; postorbital ridge strongly sinuous, posterior part crested; postorbital angle slightly produced; orbital cleft present; anterolateral margin between antennal and branchiostegal teeth slightly sinuous, with small blunt denticle; posterior part of carapace with short submedian carina aligned to submedian tooth.

Abdomen ( Fig. 14C, D) also strongly sculptured with characteristic elevations or bosses on median area and prominent protuberances derived from lateral carinae. First somite with paired, rounded tubercle on middle portion, posterior part of tergum elevated along posterior margin forming broad transverse ridge; anterior part of tergum with paired rounded tubercle laterally; two lateral protuberances present, anterior one somewhat compressed vertically. Second somite with paired, rounded prominences on middle portion; tergum with posterior part elevated in broad transverse ridge along posterior margin, and with prominent rounded protuberance on either side; two prominent protuberances present on lateral face. Third somite with middorsal carina clearly delimited, flattened on dorsal surface, constricted in anterior one-third, widened in posterior two-thirds, nearly reaching posterior margin, anterior end bilobed; some long plumose setae present on posterior part of each lateral margin of middorsal carina; two prominent lateral protuberances present, posterior protuberance further divided in two parts. Fourth somite with middorsal carina in posterior half of tergum, constricted in anterior half, narrowing in posterior half, reaching posterior margin of somite; lateral face with 1 prominent protuberance posteriorly. Fifth somite with middorsal carina tubercle-like, posterior part narrowed and extending beyond posterior margin of somite; lateral face with two prominent protuberances. Pleura of first to fifth somites rounded, unarmed. Sixth somite with elevated median carina bearing faint median sulcus; dorsolateral carina with strongly sinuous margin in dorsal view; posterodorsal margin strongly produced, distinctly bilobed, continuing to dorsolateral carinae; pleuron deeply depressed. Telson with 2 pairs of blunt dorsolateral spines, first pair located distinctly posterior to midlength.

Eye ( Fig. 14E) about as long as wide; cornea as wide as eyestalk, its width 0.2 of carapace length; eyestalk distinctly constricted, with dorsodistal protrusion not reaching distal corneal margin, bearing rounded dorsal tubercle.

Antennular peduncle ( Figs 14E, 15A) relatively stout, reaching midlength of antennal scale. First segment with short, rounded distolateral process; stylocerite broad, abruptly tapering to small blunt or subacute tooth, not reaching distolateral process of first segment, lateral margin angular proximally. Second segment with short, blunt distolateral process. Outer flagellum about half-length of peduncle, overreaching distal margin of lamella of antennal scale by 0.3–0.4 length, consisting of 5 or 6 articles.

Antenna ( Figs 14A, E, 15A) with basicerite having dorsolateral distal angle broadly rounded, ventrodistal tooth prominent, blunt. Carpocerite reaching distal 0.2 of antennal scale. Antennal scale 0.6 times as long as carapace, about 2.3 times longer than wide; lateral margin faintly sinuous; distolateral tooth moderately broad, reaching distal margin of rounded lamella.

Third maxilliped moderately stout, ultimate segment about 4.5 times longer than wide, penultimate segment about 2.1 times longer than wide ( Fig. 15B).

First pereopod ( Fig. 15C, D) with palm 2.5 times longer than wide, not narrowing distally or proximally, lateral margin slightly sinuous, mesial margin nearly straight; carpus with distolateral tooth; merus with 1 tiny dorsodistal tooth, ventral margin strongly sinuous, crested proximally. Second and third pereopods typical of genus ( Fig. 15E, F); third pereopod overreaching distal margin of antennal scale by half length of dactylus. Fourth pereopod ( Fig. 15G) moderately stout, overreaching distal margin of antennal scale by half length of dactylus; dactylus ( Fig. 15H) subspatulate with weakly convex dorsal and nearly straight ventral margins, 5.5 times longer than wide. Fifth pereopod ( Fig. 15I) with dactylus subconical, about 0.8 times as long as propodus, distinctly longer than that of fourth pereopod ( Fig. 15J); merus-ischium subequal in length to that of fourth pereopod.

Uropodal exopod with acute posterolateral tooth; no spinule mesial to posterolateral tooth ( Fig. 15K).

Eggs 1.7 x 1.2 mm; holotype carrying 13 eggs.

Male specimens unavailable.

Coloration. Not known.

Size. Largest female cl 4.8 mm, ovigerous female cl 4.7 mm.

Distribution. Known only from the Sagami Sea and Suruga Bay, central Japan ( Fig. 40); at depths of 135– 197 m.

Remarks. Metacrangon tropis n. sp. is quite distinctive in the genus in having a characteristic sculpture on the carapace and abdomen. The strongly arched rostrum with a distinctly produced distal end of the ventral carina is also unique to this new species. The distinctly carinate lateral margin of the antennal tooth of the carapace may indicate affinity of this new species to M. sinensis .

Etymology. From the Latin tropis (keel), in reference to the characteristic keels on the carapace and abdomen.