Metacrangon punctata, Komai, 2012

Komai, Tomoyuki, 2012, 3468, Zootaxa 3468, pp. 1-77 : 17-21

Metacrangon punctata n. sp.

( Figs 5–7, 43)

Material examined. Holotype. KARUBAR, stn CP 89, Banda Sea , Indonesia, 08°39’S, 131°08’E, 1084– 1058 m, 5 November 1991, ovigerous female (cl 13.5 mm), MNHN-IU-2011-5026.

Paratypes. Indonesia. KARUBAR, stn CP 87, 08°47’S, 130°49’E, 1017–1024 m, 5 November 1991, 1 female (cl 11.0 mm), MNHN-IU-2009-2097 . Papua New Guinea. BIOPAPUA, stn CP 3667, Open Bay , 04°40’S, 151°34’E, 670–921 m, 23 September 2010, 1 female (cl 12.6 mm), MNHN-IU-2011-2680; stn CP 3730, Mambare Bay, 07°51’S, 148°01’E, 750–770 m, 8 October 2010, 1 male (cl 10.6 mm), MNHN-IU-2011-1171; stn CP 3731, Mambare Bay, 07°50’S, 148°04’E, 895–1150 m, 30 October 2010, 1 female (cl 13.8 mm), MNHN-IU-2011-3261 .

Solomon Islands. SALOMON 1: stn CP 1781, 08°31.2’S, 160°37.7’E, 1036–1138 m, 29 September 2001, 1 female (cl 10.4 mm), MNHN-IU-2009.2098; stn CP 1807, 09°42.2’S, 160°52.8’E, 1077–1135 m, 2 October 2001, 1 male (cl 7.2 mm), MNHN-IU-2011-5039 .

Non-type. New Caledonia. BATHUS 1, stn CP 661, 21°05’S, 165°50’E, 960–1100 m, 13 March 1993, 1 male (cl 7.2 mm), MNHN-IU-2009-2110 .

Description. Female. Rostrum ( Figs 5A, B, E, 6A) narrowly triangular in dorsal view, somewhat ascending (angle against horizontal plane of carapace about 40°), reaching as far as antennal teeth (slightly more than 0.1 times as long as carapace); tip rounded in dorsal view; dorsal surface slightly elevated in midline; ventral surface nearly flat. Carapace ( Figs 5A, B, E, 6A) not markedly widened posteriorly even in spawning molt, 1.3 times as long as wide postorbitally; middorsal carina extending nearly to posterodorsal margin; anterior middorsal tooth elongate, styliform, arising at rostral base, obliquely erect (angle against horizontal plane of carapace about 70°), overlapping rostrum, tip reaching level of rostral tip; posterior tooth strong, arising at about 0.6 of carapace length; minute denticle present between two middorsal teeth; submedian teeth present; antennal tooth slender, acuminate, ascending in similar degree to rostrum; branchiostegal tooth strong, directed slightly laterally in dorsal view, ascending in similar degree to rostrum, overreaching dorsolateral distal angle of antennal basicerite; orbital cleft present; postorbital angle rounded; anterolateral margin between antennal and branchiostegal teeth slightly sinuous, unarmed; branchiostegal ridge reaching near to level of posterior end of hepatic groove; branchial carina distinct; branchial region coarsely punctate.

Abdomen ( Fig. 5C, D) weakly sculptured; anterior five somites each with rather broad, clearly delimited middorsal carina; middorsal carina on first somite present in middle part, those on second and third somites restricted to anterior half of tergum, anterior end of former slightly produced, that of fourth carina not extending to posterodorsal margin, that of fifth somite running over entire length, slightly produced posteriorly. Pleura of first to fifth somites each with shallow depressions laterally and accompanied by blunt ridges or elevations; first pleuron with acute or subacute ventral tooth, second pleuron with acute ventral tooth, third pleuron with bluntly pointed anteroventral angle, fourth pleuron with slightly produced anteroventral angle. Sixth somite with distinct submedian carinae; posterodorsal margin weakly bilobed; pleuron shallowly depressed, with sharp posteroventral tooth; posterolateral projection strong, terminating in acute tooth. Telson ( Fig. 5C) with 2 pairs of dorsolateral spines, anterior pair arising slightly posterior to midlength.

Eye ( Fig. 5E) slender, 1.8–1.9 times longer than wide; cornea distinctly shorter than eyestalk, corneal width less than 0.1 of carapace length; eyestalk slightly constricted, dorsodistal protrusion nearly reaching distal corneal margin, bearing blunt dorsal tubercle.

Antennular peduncle ( Figs 5E, 6A) relatively slender for genus, overreaching midlength of antennal scale. First segment with short, blunt distolateral process; stylocerite slender, terminating in blunt tip overreaching distolateral process of first segment, lateral margin gently convex. Second segment with short, blunt distolateral process. Outer flagellum overreaching distal margin of lamella of antennal scale by 0.6–0.7 length, consisting of about 15 articles.

Antennal ( Fig. 5F) basicerite with dorsolateral distal angle produced in bluntly pointed lobe, ventrolateral tooth acute. Carpocerite nearly reaching distal margin of antennal scale. Antennal scale ( Fig. 5F) 0.40–0.50 times as long as carapace and 2.9–3.0 times longer than wide; lateral margin nearly straight or faintly concave; distolateral tooth distinctly overreaching distal margin of lamella; lamella moderately broad, rounded.

First pereopod ( Fig. 6C, D) with palm 3.2 times longer than wide, not markedly widened proximally or distally, lateral and mesial margins nearly straight; carpus with distolateral tooth slightly smaller than ventrolateral tooth; merus with small dorsodistal teeth, lateral face with trace of longitudinal carina, ventral margin sinuous, bluntly carinate. Second and third pereopods typical of genus; third ( Fig. 6E) pereopod overreaching distal margin of antennal scale by half length of dactylus. Fourth pereopod ( Fig. 6F) slightly overreaching distal margin of antennal scale by half length of dactylus; dactylus ( Fig. 6G) with fringe of numerous stiff setae on margins. Fifth pereopod ( Fig. 6H) with dactylus 0.7–0.8 times as long as propodus; merus-ischium combined about 0.8 times as long as that of fourth pereopod.

Uropodal exopod with laterally pointed posterolateral tooth, but no spinule mesial to posterolateral tooth ( Fig. 6I).

Eggs 2.4 x 1.6 mm; not counted.

Male. General armature on carapace and abdomen, and abdominal sculpture slightly stronger than in females ( Fig. 7A); particularly, fourth abdominal somite with distinct anteroventral tooth. Eye about 1.7 times longer than wide ( Fig. 7B). Antennular flagellum ( Fig. 7B) distinctly longer than peduncle, overreaching distal margin of antennal scale by about 0.8 length, consisting of 15 or 16 articles (articles nearly as long as or slightly wider than long except for first article). Lateral margin of antennal scale nearly straight or faintly convex ( Fig. 7B).

Coloration. Unknown.

Size. Largest male cl 10.6 mm; largest female cl 13.8 mm, spawning molts cl 12.6–13.8 mm.

Distribution. Eastern part of the Banda and Timor Seas, Indonesia, Papua New Guinea, Solomon Islands, and New Caledonia ( Fig. 43); 670–1135 m.

Remarks. The presence of distinct middorsal carinae on the second to fourth abdominal somites and the normally developed antennal scale with a distolateral tooth distinctly overreaching the distal margin of the lamella link this new species to M. agassizii , M. bythos n. sp., and M. similis from Japan. However, M. punctata n. sp. is immediately distinguished from the allied species by the coarsely punctate branchial region of the carapace. In the other three species the branchial region is smooth. Furthermore, M. punctata differs from the latter three species in the more slender eye (1.8–1.9 times longer than the corneal width versus less than 1.5 times as long) and the more slender second segment of the antennular peduncle in females. The relatively narrow antennal scale separates M. punctata from M. agassizii (2.5–2.9 times as long as wide versus 2.1–2.4 times as long). From M. bythos , this new species further differs in the carapace not becoming wider posteriorly even in the spawning molt (vs. becoming wider posteriorly) and the more strongly produced branchiostegal teeth of the carapace.

In the feature of the ocular peduncle and antennal scale, the new species superficially resembles Metacrangon crosnieri from Madagascar, but the presence of distinct median carinae on the second to fourth abdominal somites and the more posteriorly arising posterior middorsal tooth on the carapace distinguish M. punctata from M. crosnieri .

Etymology. Named in reference to the coarsely punctate branchial region of the carapace.