Metacrangon clevai, Komai, 2012

Komai, Tomoyuki, 2012, 3468, Zootaxa 3468, pp. 1-77 : 34-38

Metacrangon clevai n. sp.

( Figs 16–18, 43)

Type material. Holotype. SALOMON 1, stn CP 1753, Solomon Islands, 09°02.7’S, 159°49.4’E, 1001–1012 m, 26 September 2001, female (cl 10.4 mm), MNHN-IU-2009-2099.

Paratypes. Solomon Islands: SALOMON 1, stn CP 1752, 09°06.9’S, 159°53.2’E, 896–912 m, 25 September 2001, 1 male (cl 5.4 mm), MNHN-IU-2009-2100 . Vanuatu: BOA 1, stn CP 2425, Big Bay , 14°53.50’S, 166°51.30’E, 777 m, 7 September 2005, 1 male (cl 7.5 mm), MNHN-IU-2009-2101; stn CP 2434, Big Bay, 14°53.90’N, 166°51.50’E, 980–1040 m, 9 September 2005, 1 male (cl 6.5 mm), MNHN-IU-2009-2102 .

Description. Female. Rostrum ( Figs 16A, B, E, 17A) triangular in dorsal view, directed forward, extending as far as antennal teeth (about 0.1 times as long as carapace); tip rounded in dorsal view; dorsal surface with slightly elevated lateral margins; ventral carina low. Carapace ( Figs 16A, B, E, 17A) not markedly widened posteriorly even in spawning molt, slightly longer than wide postorbitally; middorsal carina extending nearly to posterodorsal margin, bearing two slightly unequal, strongly compressed middorsal teeth; anterior tooth broad, epigastric in position, arising at 0.1 of carapace length, not reaching base of rostrum; posterior tooth slightly smaller than anterior tooth, arising slightly posterior to midlength of carapace; no denticle present between two middorsal teeth; submedian teeth absent; antennal tooth directed forward in lateral view, acuminate; orbital cleft present; postorbital angle rounded; anterolateral margin between antennal and branchiostegal teeth nearly straight, unarmed; branchiostegal tooth strong, directed forward in dorsal view, strongly compressed dorsoventrally, somewhat ascending in lateral view (angle about 40° against horizontal plane of carapace), distinctly overreaching dorsolateral distal angle of antennal basicerite; branchiostegal carina not reaching level of posterior end of hepatic groove; branchial ridge absent.

Abdomen ( Fig. 16C, D) slightly sculptured. First and second somites rounded dorsally; third somite with trace of middorsal carina; fourth somite with weakly delimited, broad middorsal carina; fifth somite with broad, clearly delimited middorsal carina confluent with anterior transverse carina and not reaching posterodorsal margin. Fourth and fifth somites with obsolete lateral carinae. Pleura of anterior three somites rounded, fourth pleuron with rounded anteroventral angle. Sixth somite with distinct, concave submedian carinae; posterodorsal margin slightly bilobed; pleuron shallowly depressed, with sharp posteroventral tooth; posterolateral process terminating in acute tooth. Telson ( Fig. 16C) damaged, but bearing 2 pairs of dorsolateral spines.

Eye ( Fig. 16E) moderately slender, about 1.5 times longer than wide; cornea as wider as eyestalk, its width about 0.1 of carapace length; eyestalk with dorsodistal protrusion not reaching distal corneal margin, bearing rounded dorsal tubercle.

Antennular peduncle ( Figs 16E, 17A) moderately stout, reaching midlength of antennal scale. First segment with short, blunt distolateral process; stylocerite abruptly tapering to subacute tooth, reaching distolateral process of first segment of antennular peduncle, lateral margin gently convex. Second segment widened distally, with short, blunt distolateral process. Outer flagellum subequal in length to peduncle, overreaching distal margin of lamella of antennal scale by 0.4 length, consisting of 13 articles.

Antenna ( Figs 16E, 17A) with basicerite having dorsolateral distal angle produced in rounded lobe, ventrodistal tooth acute. Antennal scale about 0.4 times as long as carapace and about 1.9 times longer than wide; lateral margin nearly straight; distolateral tooth moderately broad, reaching distal margin of broadly rounded lamella.

Third maxilliped relatively slender; ultimate segment gradually tapering distally, about 5.8 times longer than wide; penultimate segment about 2.6 times longer than wide ( Fig. 17B).

First pereopod ( Fig. 17C, D) moderately stout; palm 3.1 times longer than wide, not markedly widened proximally or distally, lateral margin faintly sinuous, mesial margin nearly straight; carpus with dorsolateral tooth; merus with 1 small dorsodistal teeth, ventral margin sinuous, sharply crested. Second and third pereopods typical of genus ( Fig. 17E, F); third pereopod overreaching distal margin of antennal scale by length of distal two segments. Fourth pereopod ( Fig. 17G) relatively slender, reaching distal margin of antennal scale by tip of dactylus; dactylus ( Fig. 17H) spatulate with convex dorsal and straight ventral margins, about 4.0 times longer than broad. Fifth pereopod ( Fig. 17I) with slender, subspatulate dactylus, about 0.7 times as long as propodus ( Fig. 17J); merus-ischium combined about 0.7 times as long as that of fourth pereopod.

Uropodal exopod with laterally pointed posterolateral tooth and spinule mesial to posterolateral tooth ( Fig. 17K).

Male. Carapace ( Fig. 18A) with branchiostegal tooth less ascending than in females; outer antennular flagellum ( Fig. 18B) longer than peduncle, consisting of 12 or 13 articles (articles as wide as or slightly wider than long except for first article). Intact telson with first pair of dorsolateral spines situated slightly posterior to midlength. Appendix masculina typical of genus, as illustrated ( Fig. 18C).

Coloration. Not known.

Size. Largest male cl 7.5 mm; female cl 10.4 mm (spawning molt).

Distribution. Solomon Islands and Vanuatu ( Fig. 43); 777–1040 m.

Remarks. Metacrangon clevai n. sp. is readily distinguished from all other members of the M. munita group except for M. trigonorostris by the lack of submedian teeth on the carapace. From M. trigonorostris , it differs in many respects, including the dorsoventrally flattened and forwardly directed rostrum, the possession of two middorsal teeth on the carapace, the acute branchiostegal tooth, the presence of distolateral processes on the first and second segments of the antennular peduncle, and the relatively wide antennal scale with a straight lateral margin. In M. trigonorostris , the rostrum is obliquely directed with a high ventral carina; there is only one middorsal tooth in the cardiac position on the carapace; the branchiostegal tooth is subacute at most; the proximal two segments of antennular peduncle lacks development of distolateral process; and the lateral margin of the antennal scale is concave. It appears that the two species are not closely related despite sharing a character unusual for the genus.

The two male specimens from Vanuatu are parasitized by unidentified bopyrid isopods .

Etymology. This new species is dedicated to Régis Cleva of MNHN for his contributions to the taxonomy of decapod crustaceans and for his generous help to his colleagues.