Metacrangon latirostris, Komai & Chan, 2020

Komai, Tomoyuki & Chan, Tin-Yam, 2020, New records of the crangonid shrimp genus Metacrangon Zarenkov, 1965 (Decapoda: Caridea), from the south of Java, eastern Indian Ocean, with description of a new species, Raffles Bulletin of Zoology 68, pp. 326-333 : 326-330

publication ID	https://doi.org/ 10.26107/RBZ-2020-0026
publication LSID	lsid:zoobank.org:pub:8F396044-E58D-4582-9A50-262AE353B9FD
persistent identifier	https://treatment.plazi.org/id/5EE7AD8C-B3F5-4505-81DD-94CC8D3B0ECB
taxon LSID	lsid:zoobank.org:act:5EE7AD8C-B3F5-4505-81DD-94CC8D3B0ECB
treatment provided by	Carolina
scientific name	Metacrangon latirostris
status	sp. nov.

Treatment

Metacrangon latirostris , new species

( Figs. 1 View Fig , 2 View Fig , 4A View Fig )

Material examined. Holotype: female (cl 9.4 mm), SJADES, stn CP 47, S of Java, 07°47.97′S, 107°45.30′E to 07°48.26′S, 107°45.71′E, 530– 476 m, 1 April 2018, beam trawl, MZB Cru 5054. GoogleMaps

Diagnosis. Rostrum 0.1 times carapace length, falling far short of distal corneal margins, broadly triangular in dorsal view (distinctly wider than long), directed forward, tip blunt. Carapace with anterior middorsal spine moderately large, strongly compressed laterally, postrostral in position (arising at rostral base), reaching midlength of rostrum; posterior middorsal spine arising at 0.6 of carapace length, distinctly more slender than anterior middorsal spine; gastric region with submedian spines; shallow orbital cleft discernible; antennal spine directed forward in dorsal view, weakly ascending in lateral view; branchiostegal spine moderately strong, directed forward in dorsal view. Pleomeres 1–4 without trace of middorsal carina, pleomere 5 with faint middorsal carina; pleura of pleomeres 1–3 without conspicuous tooth or spine marginally; pleomere 6 with rather obsolescent submedian carinae. Telson with posteromedian process moderately produced, subacute. Eyestalk (including cornea) slightly longer than wide; dorsal tubercle relatively small, rounded, papilla-like. Antennular peduncle reaching midlength of antennal scale; article 1 with stylocerite reaching slightly beyond short, blunt distolateral process; article 2 also with short, blunt distolateral process. Antennal scale 0.4 times as long as carapace, 2.2 times as long as wide; lateral margin faintly sinuous; distolateral spine reaching as far as rounded distal lamella. Maxilliped 3 with ultimate article 7.2 times as long as wide. Pereopod 1 palm 3.9 times as long as wide.

Description. Female (holotype). Body ( Fig. 1 View Fig ) robustly built as in other congeneric species; integument firm.

Rostrum ( Figs. 1A, B View Fig , 2A View Fig ) broadly triangular in dorsal view, distinctly wider than long, directed forward, falling slightly short of antennal spines and falling far short of distal corneal margins, 0.1 times as long as carapace; tip rounded in dorsal view; lateral margins not particularly upturned; ventral surface medially bluntly carinate, with tuft of plumose setae subterminally. Carapace ( Figs. 1A, B View Fig , 2A View Fig ) 1.3 times as long as wide, surface covered by very short setae; middorsal carina extending from rostral base to posterior one-fourth, bearing two unequal spines; anterior middorsal spine moderately large, strongly compressed laterally, tooth-like, postfrontal in position (arising at base of rostrum), extending to midlength of rostrum; posterior spine distinctly more slender than anterior spine, cardiac in position (arising at 0.6 of carapace length); no minute denticle present between two middorsal spines; gastric region delimited by low, blunt postorbital carinae and posterior transverse ridges, particularly depressed posterior to rostral base, with pair of moderately small submedian spines arising at midlength of carapace; antennal spine relatively large, directed forward in dorsal view, slightly ascending in lateral view; postorbital angle broadly rounded, orbital cleft distinct; anterolateral margin between antennal and branchiostegal spines slightly concave, with minute denticle inferior to base of antennal spine; branchiostegal spine moderately strong, directed forward in dorsal view, slightly ascending in similar degree to antennal spine in lateral view, just reaching dorsolateral distal angle of antennal basicerite; branchiostegal carina not reaching to level of hepatic spine; hepatic spine moderate in size, accompanied with shallow hepatic groove inferior to its base; branchial carina absent; pterygostomial margin folded beneath branchiostegal spine, with minute pterygostomial spine.

Pleon ( Fig. 1 View Fig B–D) not very sculptured, widest at anterior end of pleomere 1. Pleomeres 1–4 dorsally rounded, without trace of middorsal carina; pleomere 5 with obsolescent middorsal carina. Tergites of pleomeres 2–5 not elevated along posterior margins. Pleura of anterior three somites rounded, pleuron 4 with posteriorly margin produced but rounded; pleuron 5 with angular posteroventral margin, but without spine. Pleomere 6 with obsolescent, parallel submedian carinae, falling far short of posterodorsal margin; posterodorsal margin produced, weakly bilobed; dorsolateral carina distinct; pleuron shallowly depressed; posterolateral process abruptly terminating in small acute spine. Telson ( Fig. 1E View Fig ) 1.7 times as long as pleomere 6, with 2 pairs of tiny dorsolateral spiniform setae, first pair located posterior to midlength; dorsal surface medially grooved; posteromedian process moderately produced, triangular, subacutely pointed, flanked by 1 pair of minute spiniform setae.

Thoracic sternum widened posteriorly. Sternite 5 with anteriorly directed, slender median spine. Sternites 6–8 each with median keel terminating anteriorly in small spine. Pleonal tergites 1–4 each with ventrally directed median spine becoming shorter posteriorly, tergite 5 with low median carina.

Eyestalk ( Figs. 1A, B View Fig , 2A View Fig ) stout, slightly longer than wide, somewhat constricted medially; dorsodistal protrusion not reaching distal corneal margin, bearing small papilla-like tubercle; cornea hemispherical, as wide as eyestalk, corneal width 0.12 of carapace length.

Antennular peduncle ( Figs. 1A, B View Fig , 2A View Fig ) moderately stout, slightly reaching midlength of antennal scale. Article 1 with short, blunt distolateral process; stylocerite reaching slightly beyond distolateral process of article 1, terminating in inwardly curved blunt spine, lateral margin evenly convex. Article 2 with short, blunt distolateral process. Article 3 very short. Outer flagellum overreaching distal margin of antennal scale by half length, consisting of 11 or 12 articles; inner flagellum slightly longer than outer flagellum.

Antenna ( Figs. 1A, B View Fig , 2A View Fig ) with basicerite having dorsolateral distal angle produced in subacutely pointed process, ventrolateral distal spine exceeding as far as dorsolateral distal process. Antennal scale (scaphocerite) 0.4 times as long as carapace and 2.2 times as long as wide; lateral margin faintly sinuous; distolateral spine relatively slender, just reaching rounded distal margin of lamella. Carpocerite falling slightly short of distal margin of distal lamella of antennal scale.

Maxilliped 3 ( Fig. 2B, C View Fig ) overreaching distal margin of antennal scale by full length of ultimate article, with setation typical of genus (omitted in Fig. 2B, C View Fig ). Coxa with rounded lateral plate. Antepenultimate article slightly sinuous in dorsal view, with 1 subdistal spiniform seta on ventral surface ( Fig. 2D View Fig ). Penultimate article (= carpus) 3.2 times as long as wide, with 1 long spiniform setae at distomesial angle and dense, stiff grooming setae entirely on mesial face. Ultimate article flattened, spatulate, 7.2 times as long as wide; mesial margin with long spiniform setae in individual or sets of 2 or more, mixed with long stiff setae.

Pereopod 1 ( Fig. 2E, F View Fig ) moderately stout. Ischium short, obliquely articulated to merus. Merus armed with small dorsodistal spine; ventral margin faintly sinuous, sharply crested. Carpus short, subglobular, armed with 1 small spine on lateral margin in addition to small ventrolateral distal spine. Palm 3.9 times as long as wide, not markedly widened proximally or distally; lateral margin faintly sinuous, mesial margin nearly straight; carpus with dorsolateral tooth; occlusal margin strongly oblique, gently convex, with submarginal row of sparse setae; fixed finger moderately slender, acuminate. Dactylus gently curved, tip not exceeding base of fixed finger when closed.

Pereopod 2 ( Fig. 2G View Fig ) just reaching distal margin of scaphocerite. Coxa with prominent, sickle-like projection. Ischium arcuate, slightly shorter than merus. Carpus subequal in length to merus. Chela 0.6 times as long as propodus, with elongate palm; dactylus 0.3 times as long as palm.

Pereopod 3 ( Fig. 2I View Fig ) overreaching distal margin of scaphocerite by length of dactylus and 0.3 of propodus; length ratio of ischium to dactylus 3.3: 3.1: 4.4: 2.9: 1.

Pereopod 4 ( Fig. 2H View Fig ) damaged, only left preserved. Ischium and merus moderately slender, with row of long setae on dorsal margin, shorter setae also on ventral margin. Carpus subcylindrical, also with row of long setae on dorsal margin. Propodus and dactylus missing.

Pereopod 5 missing on either side.

Pleopods without distinguishing features; setose, carrying eggshells after hatching. Uropod with protopod having weakly bilobed posterior margin; endopod falling short of tip of telson; exopod slightly shorter than endopod, with small triangular posterolateral spine ( Fig. 1G View Fig ).

Etymology. The name “ latirostris ” (the Latin “ latus ” = broad + “ rostris ” = rostrum) refers to the characteristic broad rostrum of the new species in the genus.

Colouration in life. Body generally brownish, margins of middorsal spines on carapace white; antennular and antennal peduncles and maxilliped 3 similarly brownish; pereopods paler, semitransparent; pleopods also semitransparent.

Distribution. Known only from south of Java, Indonesia, at depths of 476– 530 m.

Remarks. Two informal species groups, viz., “ Metacrangon munita ( Dana, 1852) ” species group and “ M. jacqueti (A. Milne-Edwards, 1881) ” species group, have been recognised in Metacrangon (cf. Yaldwyn, 1960; Komai, 1997, 2012). Metacrangon latirostris , new species, belongs to the “ M. munita ” group for having marginally rounded, unarmed pleura of the pleomeres 1–3 and the moderately strong, not particularly enlarged anterior middorsal spine on the carapace. The new species is unique in the “ M. munita ” species group in combination of the following characters: (1) the rostrum is distinctly wider than long ( Figs. 1A View Fig , 2A View Fig ); and (2) the anterior middorsal spine on the carapace is postrostral in position, with the tip reaching the midlength of the rostrum ( Fig. 1A, B View Fig ). The new species appears close to M. clevai , which was also collected by SJADES 2018. Other than the distinguishing characters stated above, M. latirostris , new species, can further be separated from M. clevai by the presence of paired submedian spines on the gastric region of the carapace and the more posteriorly arising posterior middorsal spine on the carapace (arising at 0.6 of the carapace length rather than at about half length of the carapace). In M. clevai , the rostrum is longer than wide to as long as wide; the anterior middorsal spine is located in an epigastric position, falling short of the rostral base; and there are no submedian spines on the gastric region ( Fig. 3 View Fig ; Komai, 2012, figs. 16, 18).