Metacrangon australis, Komai & Taylor, 2010

Komai, T. & Taylor, J., 2010, Three new species of the crangonid genus Metacrangon Zarenkov (Crustacea: Decapoda: Caridea) from Australia, Memoirs of Museum Victoria 67, pp. 45-59 : 46-49

Metacrangon australis sp. nov.

Figures 1–3

Material examined. Holotype: Australia, Tasmania, southwestern Pacific west of Macquarie Island (54°42.42'S, 158°45.12'E – 54°41.36'S, 158°43.12'E), 700–900 m, 22–23 Jan 1999, FRV Southern Surveyor , epibenthic sled (stn SS01/99/65), NMV J60424 (1 female, cl 13.1 mm).

Paratypes: same data as holotype, NMV J61200 (2 females, cl 9.9, 12.1 mm) .

Description. Body (fig. 1) moderately robust. Rostrum (figs 2a–b) narrowly triangular with acute apex in dorsal view, directed forward or slightly ascending, about 0.20 times as long as carapace; dorsal surface with middorsal carina in proximal half; lateral margin slightly convex in lateral view, merging into orbital margin; midventral carina distinct, ventral margin nearly straight in lateral view. Carapace (figs 1, 2a) very slightly widened anteriorly, longer than wide postorbitally; surface covered with very short setae; dorsal midline with two moderately small, subequal teeth; anterior (epigastric) tooth arising at 0.10 of carapace length, posterior (cardiac) tooth broken off, arising at 0.75–0.80 of carapace length; submedian and hepatic teeth moderately small; antennal tooth moderately strong, directed forward in dorsal view, weakly ascending (same degree as rostrum) in lateral view, acuminate, falling short of rostral tip; orbital cleft absent; anterolateral margin between antennal and branchiostegal teeth sinuous with obtuse lobule (holotype) or with tiny denticle (paratypes) inferior to base of antennal tooth; branchiostegal tooth moderately strong, very slightly diverging anteriorly in dorsal view and strongly ascending in lateral view, distinctly overreaching dorsodistal margin of antennal basicerite; pterygostomial tooth small, visible in lateral view; postorbital carina clearly delimited, accompanied by longitudinal suture; weak epibranchial carina present.

Thoracic sternites depressed; fifth sternite with small, forwardly directed median tooth, otherwise unarmed.

Abdomen (figs 1, 2c) moderately sculptured; first to fifth somites with sharply delimited, crested middorsal carina, anterior end of middorsal carina on second somite produced anteriorly. Pleuron of anterior four somites rounded marginally. Fifth somite with posterodorsal margin slightly produced medially; posterolateral margin unarmed; pleuron with posteroventral angle rounded, ventral margin gently convex. Sixth somite 1.6 times longer than wide, with distinct, slightly curved submedian carinae, not reaching posterodorsal margin; dorsolateral carina distinct, reaching to posterodorsal margin; posterodorsal margin produced, distinctly bilobed; pleuron flared laterally, with small posteroventral tooth; posterolateral process moderately strong, directed posteriorly, terminating in sharp tooth. Telson (figs 2c–d) tapering distally to acute apex, with three pairs of minute dorsolateral spines, anteriormost pair located at posterior 0.35; three pairs of spiniform setae posterior to third pair of dorsolateral spines.

Eye (figs 2a–b) as long as wide; cornea as wide as eyestalk, darkly pigmented, corneal width 0.13–0.15 of carapace length; eyestalk with small, papilla-like dorsal tubercle.

Antennular peduncle (figs 2a–b) moderately stout, reaching midlength of antennal scale. First segment with prominent, blunt distolateral process directed dorsally; distomesial margin unarmed; stylocerite falling far short of distolateral process of first segment, terminating in slender, sharp tooth, lateral margin gently convex. Second segment widened distally, slightly longer than wide, with prominent, blunt distolateral process. Third segment much wider than long. Outer flagellum consisting of 13 articles.

Antennal basicerite (figs 2a–b) stout, with acutely pointed dorsodistal lateral angle and long ventrolateral tooth distinctly overreaching dorsodistal lateral angle. Antennal scale (figs 2a–b) 0.50–0.55 times as long as carapace and about 2.3 times longer than wide; lateral margin weakly concave; distolateral tooth moderately broad, slightly overreaching rounded lamella.

Third maxilliped (fig. 3a) relatively stout, overreaching antennal scale by full length of ultimate segment; ultimate segment about 4.5 times longer than wide; penultimate segment about 2.3 times longer than wide; antepenultimate segment with two subequal spiniform setae subdistally (fig. 3b).

First pereopod (fig. 3c) moderately stout, slightly overreaching antennal scale; palm (fig. 3d) 2.9 times longer than wide, not widened proximally or distally; lateral and mesial margins faintly sinuous; thumb relatively long; carpus with small ventrolateral tooth, otherwise unarmed on distolateral margin; merus with small dorsodistal tooth, ventral margin sinuous, crested. Second pereopod with dactylus about 0.3 times as long as palm (fig. 3e); length ratio of chela to ischium 1:2.3:2.2:1.8. Third pereopod (fig. 3f) slender; length ratio of dactylus to ischium 1:1.8:3.8:2.8:2.8. Fourth pereopod (fig. 3g) relatively stout, reaching nearly distal margin of antennal scale; dactylus (fig. 3H) elongate subovate, spatulate, about 0.5 times as long as propodus, margins naked; dactylus–propodus articulation about 60°; propodus about 4.0 times longer than wide; propodus–carpus combined distinctly shorter than merus–ischium combined. Fifth pereopod (fig. 3i) shorter than fourth pereopod; dactylus (fig. 3j) spatulate, subequal in length to dactylus of fourth pereopod, about 0.7 times as long as propodus.

Uropodal exopod with blunt posterolateral tooth and with three spiniform setae (fig. 3k).

Colouration. Not known.

Distribution. Known only from the type locality in the Southern Ocean southeast of Tasmania, west of Macquarie Island, at depths of 700– 900 m.

Remarks. Metacrangon australis is somewhat similar to M. proxima , M. variabilis and M. poorei sp. nov. in the general disposition of carapacial teeth and the carination of the abdomen, but it is quite unique within the genus in having the combination of the following characters: the rostrum is narrowly triangular and distinctly overreaches the distal corneal margins; the carapace has two middorsal teeth, of them the anterior tooth is distinctly postrostral and the posterior (cardiac) tooth arises at 0.75–0.80 of the carapace length; the lateral margin of the rostrum merges into the orbital margin, thus no cleft is defined; the first to fifth abdominal somites bear sharp, crested middorsal carina; and the anterior three pleura are rounded marginally. Of particular note is the lack of an orbital cleft, an uncommon trait previously known only in M. knoxi ( Yaldwyn, 1960) (see Komai, 1997). M. knoxi is referred to the M. jacqueti (A. Milne-Edwards, 1881) species group ( Komai, 1997) and is readily distinguished from M. australis by the anterior middorsal tooth on the carapace that arises at the midlength of the rostrum and the presence of a ventral tooth on each first to third abdominal pleuron.

Etymology. Named ‘ australis ’, Latin meaning ‘southern’, alluding to the type locality of this new species, representing the southernmost locality of the genus.