Metacrangon teina, Komai & Ahyong, 2010

Komai, Tomoyuki & Ahyong, Shane T., 2010, The crangonid shrimp genus Metacrangon (Crustacea: Decapoda: Caridea) from New Zealand, with descriptions of four new species, Journal of Natural History 45 (1 - 4), pp. 77-111 : 95-102

Metacrangon teina sp. nov.

( Figures 11–15)

Material examined

Holotype. Challenger Plateau, 39 ◦ 32.61 ′ S, 169 ◦ 42.87 ′ E, 636– 634 m, beam trawl, TAN0707 / 93, 4 June 2007, female (CL 7.0 mm), NIWA 33204 .

Paratypes. Challenger Plateau, same data as holotype, three females (CL 5.6–6.1 mm, largest with epicaridean), NIWA 42687 ; 41 ◦ 35.09 ′ S, 170 ◦ 34.49 ′ E, 498–500 m, stn V0429 , 11 September 1992, one female (CL 6.4 mm), NIWA 11569 ; 42 ◦ 34.00 ′ S, 170 ◦ 19.90 ′ E, 600 m, stn V0424 , 9 September 1992, one male (CL 5.2 mm), NIWA 11583 ; Foveaux Strait, 46 ◦ 39.00 ′ S, 167 ◦ 04.99 ′ E, 320–333 m, stn Z2378, 20 April 1971, one female (CL 7.3 mm), NIWA 58582 .

Description

Body ( Figures 11, 12A,C ) moderately robust. Rostrum ( Figure 12A,B,D ) dorsoventrally flattened, triangular with acute apex in dorsal view, directed forward, 0.20–0.25 times as long as carapace; dorsal surface shallowly sulcate; lateral margin arched in lateral view, merging into orbital margin; midventral carina low, sharply delimited, ventral margin slightly sinuous in lateral view. Carapace ( Figures 11, 12A ) not widened posteriorly, distinctly longer than wide postorbitally; surface covered with very short setae; dorsal midline with two prominent teeth; anterior tooth relatively small for M. jacqueti species group, arising at midlength of rostrum, weakly to strongly ascending, overlapping rostrum, subequal to or distinctly larger than posterior (cardiac) tooth, tip reaching rostral apex; posterior (cardiac) tooth sometimes hooked, arising at 0.65–0.70 of CL; submedian tooth relatively small; hepatic tooth relatively small, followed by clearly delimited epibranchial carina; antennal tooth small, directed forward in dorsal view, slightly ascending in lateral view, acuminate, far falling short of rostral apex; orbital cleft absent; anterolateral margin between antennal and branchiostegal teeth concave, with tiny denticle inferior to base of antennal tooth; branchiostegal tooth moderately strong, directed slightly to somewhat laterally in dorsal view ( Figures 12A , 15A ) and slightly dorsally in lateral view, reaching beyond dorsodistal margin of antennal basicerite; pterygostomial tooth small, not visible in lateral view; postorbital carina obsolete, accompanied by longitudinal suture; epibranchial carina distinct.

Abdomen ( Figures 11, 12C ) barely sculptured; anterior two somites with trace of mid-dorsal carina anteriorly, third somite rounded or with faint trace of middorsal carina, and fourth somite with trace of mid-dorsal carina. First and second pleura each with blunt tooth medially on ventral margin; third pleuron with blunt tooth at anteroventral angle; fourth pleura unarmed. Fifth somite with low, but well delineated mid-dorsal carina; posterodorsal margin slightly produced medially; posterolateral margin unarmed; pleuron with posteroventral angle bluntly pointed or rounded; ventral margin slightly sinuous. Sixth somite with distinct, slightly curved submedian carinae, not reaching posterodorsal margin; dorsolateral carina distinct, reaching nearly to posterodorsal margin; posterodorsal margin produced, faintly bilobed; pleuron flared laterally, posteroventral tooth moderately strong, acute or subacute; posterolateral process strong, somewhat curved laterally, terminating in sharp tooth. Telson ( Figure 14C ) longer than sixth somite, gradually tapering posteriorly to acute apex; dorsal surface grooved mesially, with three pairs of dorsolateral spines, first pair located at about posterior 0.3.

In spawning moults, thoracic sternum concave, armature absent; only fifth sternite with small tubercles medially; first to fourth abdominal sternites unarmed, fifth sternite with low median tubercle. In male and pre-spawning moults of females ( Figure 14B ), fifth thoracic sternite with sharp, procurved tooth; sixth to seventh somites each with rounded, strongly compressed prominence, becoming higher posteriorly; first to fourth abdominal sternites armed each with median tooth. Sixth abdominal sternite shallowly depressed medially.

Eye ( Figure 12A,D ) as long as wide or slightly wider than long; cornea as wide as eyestalk, light brown or opaque in preservative, corneal width 0.20–0.25 of CL; eyestalk with small, papilla-like dorsal tubercle.

Antennular peduncle ( Figure 12A,D ) relatively stout, slightly falling short of midlength of antennal scale. First segment with prominent, bluntly pointed distolateral process directed dorsally; distomesial margin unarmed; stylocerite nearly reaching distolateral process, acutely pointed, lateral margin gently convex. Second segment distinctly widened distally, with prominent, blunt distolateral process. Third segment much wider than long. Outer flagellum slightly over-reaching distal margin of lamella of antennal scale, consisting of 9 or 10 articles in females (in male specimen, flagella broken off).

Antennal basicerite ( Figure 12A,D ) stout, with sharply pointed dorsodistal lateral angle and short ventrolateral tooth slightly over-reaching dorsodistal lateral angle; carpocerite subcylindrical, reaching distal 0.20 of antennal scale. Antennal scale about 0.50 times as long as carapace and 2.0 times longer than wide; lateral margin nearly straight; distolateral tooth moderately wide, slightly over-reaching rounded distal margin of lamella.

Third maxilliped relatively slender, over-reaching antennal scale by 0.6 length of ultimate segment; margins and dorsal surface of distal two segments with numerous short to long setae; ultimate segment ( Figure 13A ) gradually tapering distally, 7.5– 8.0 times longer than wide; penultimate segment about 3.5 times longer than wide; antepenultimate segment sinuously curved in dorsal view, with thick tuft of long setae dorsodistally; ventral surface unarmed; exopod far falling short of distal margin of antepenultimate segment, with well-developed flagellum.

First pereopod ( Figure 13B,C ) moderately stout, reaching distal margin of antennal scale; palm 3.5–3.7 times longer than wide, not widened proximally or distally, cutting edge oblique; lateral and mesial margins nearly straight; thumb moderately broad; carpus with small ventrolateral tooth, otherwise unarmed on lateral margin; merus with one small dorsodistal tooth, ventral margin sinuous, crested. Second pereopod ( Figure 13D ) chelate, reaching nearly to midlength of antennal scale; dactylus about 0.5 times as long as palm; cutting edges of fingers minutely pectinate; length ratio of chela to ischium 1: 1.8: 1.7: 1.4; coxa with prominent flap-like process (not figured). Third pereopod ( Figure 13E ) slender, nearly reaching distal margin of antennal scale by tip of dactylus; length ratio of dactylus to ischium 1: 1.7: 2.8: 2.2: 2.5. Fourth pereopod ( Figure 12F ) moderately stout, slightly over-reaching midlength of antennal scale by dactylus; dactylus ( Figure 13G ) narrowly spatulate, about 0.8 times as long as propodus, margins naked; dactylus–propodus articulation about 45 ◦; propodus about 4.2 times longer than wide, bearing row of stiff setae on dorsal and ventral margins; carpus shorter than propodus, with sparse setae on dorsal margin; merus with faint ridge on lateral surface; ischium slightly shorter than merus; row of long setae on dorsal and ventral margins of merus and ischium (dorsal setae longer than ventral setae). Fifth pereopod ( Figures 13H , 14D ) distinctly shorter than fourth pereopod, falling short of base of branchiostegal tooth or only slightly over-reaching distal margin of merus of fourth pereopod; dactylus subspatulate, but more slender than that of fourth pereopod, about 0.9 times as long as propodus; setation much less than in fourth pereopod.

Male second pleopod with appendix masculina short, bearing several setae.

Uropod not reaching tip of telson; exopod with nearly straight lateral margin, posterolateral tooth acute ( Figure 13I ); minute spinule mesial to posterolateral tooth; endopod longer and narrower than exopod.

Colouration in life

Not known.

Size

Largest female at spawning moult, CL 7.3 mm; only known male CL 5.2 mm. Distribution

Known only from New Zealand: Challenger Plateau, at depths of 498–636 m ; Foveaux Strait , 320–333 m.

Etymology

Named after the Maori word “ teina ”, meaning younger brother or sister, in reference to the close relationship to M. knoxi ; used as a noun in apposition.

Figures

Figure 12. Metacrangon teina sp. nov., holotype, female (CL 7.0 mm), NIWA 33204. (A) Carapace and cephalic appendages, dorsal view (setae partially omitted); (B) anterior part of carapace, lateral view (setae omitted); (C) abdomen, dorsal view (telson damaged; setae omitted); (D) right side of anterior part of carapace, eye and antennae, dorsal view (setae partially omitted). Scale bars: 2 mm for A, C; 1 mm for B, D.

Figure 13. Metacrangon teina sp. nov., holotype, female (CL 7.0 mm), NIWA 33204. Left appendages. (A) Distal two segments of third maxilliped, ventral (flexor) view; (B) first pereopod, lateral view; (C) same, subchela, ventral (flexor) view; (D) second pereopod, lateral view; (E) third pereopod, lateral view; (F) fourth pereopod, lateral view; (G) same, dactylus, flexor view; (H) fifth pereopod (dactylus and propodus missing); (I) posterolateral part of uropodal exopod. Scale bars: 1 mm for A–F, H; 0.5 mm for G, I.

Figure 14. Metacrangon teina sp. nov., paratype, female (CL 5.8 mm), NIWA 42687. (A) Carapace, lateral view; (B) armature of fifth to eighth thoracic sternites, left ventrolateral view; (C) telson, dorsal view; (D) merus and ischium of fourth pereopod and entire fifth pereopod, right side, lateral view. Scale bars: 2 mm for A; 1 mm for B–D.

Figure 15. Metacrangon teina sp. nov., paratype, male (CL 5.2 mm), NIWA 11583. (A) Anterior part of carapace and cephalic appendages, dorsal view (left branchiostegal tooth, antennular flagella and left antennal scale broken off); (B) endopod of left second pleopod. Scale bar: 1 mm for A, 0.25 mm for B.