Metacrangon richardsoni ( Yaldwyn, 1960 )

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 : 103-107

Metacrangon richardsoni ( Yaldwyn, 1960)

( Figures 17 , 18 )

Sclerocrangon n. sp. – Richardson and Yaldwyn 1958, p 40, fig. 42.

Sclerocrangon richardsoni – Yaldwyn, 1960, p. 39, fig. 8 [type locality: Palliser Bay , Cook Strait, 41 ◦ 42.5 ′ S, 175 ◦ 09 ′ E, 1007 m] .

Material examined

Holotype. Palliser Bay , Cook Strait, North Island, 41 ◦ 42.5 ′ S, 175 ◦ 09.0 ′ E, 1007 m, mud with shell, rock and gravel, VUZ83, beam trawl, 17 February 1957, CL 8.9 mm (10.1 mm including rostrum), NMZ Cr000782.

Non-type. Hikurangi Margin , Waiarapa Seep (North Tower), TAN0616 / 79, 41 ◦ 46.95– 46.83 ′ S, 175 ◦ 23.98–24.25 ′ E, 1040–1053 m, RV Tangaroa , 13 November 2006, one female (CL 11.8 mm), NIWA 29392 .

Abbreviated description

Body ( Figure 17 ) robust. Rostrum ( Figures 17A,B , 18A ) somewhat ascending, narrowing anteriorly; distal margin generally rounded, with minute point terminally; dorsal surface faintly carinate on midline; lateral margin gently arched in lateral view, continuing to postorbital carina; midventral carina relatively row, ventral margin nearly straight. Carapace ( Figure 17A,B ) slightly longer than wide postorbitally; orbital margin with distinct cleft; anterior mid-dorsal tooth relatively large, compressed laterally, epigastric in position, arising at 0.10 of CL; posterior mid-dorsal tooth subequal in size to anterior mid-dorsal tooth, arising at 0.53 of CL; submedian and hepatic teeth moderately small; antennal tooth acuminate, slightly falling short of level of rostral apex, directed forward in dorsal view, slightly ascending in lateral view; branchiostegal tooth moderately strong, directed forward in lateral view, slightly ascending in lateral view; no denticle on anterolateral margin between antennal and branchiostegal teeth; postorbital carina low, blunt; epibranchial carina absent.

First to fourth abdominal somites rounded dorsally, fifth somite with broad, clearly delimited mid-dorsal carina ( Figure 17D–F ). First to third abdominal pleura rounded marginally, posteroventral margin of fourth pleuron rounded, that of fifth pleuron with acute posteroventral tooth. Sixth abdominal somite ( Figure 17G ) with distinct submedian and dorsolateral carinae.

Eye ( Figures 17B , 18A ) slightly longer than wide; cornea darkly pigmented, as wide as eyestalk, corneal width 0.12 of CL; eyestalk with papilla-like dorsal tubercle. Antennular peduncle ( Figures 17B , 18A ) moderately stout, reaching midlength of antennal scale; first segment with prominent, blunt distolateral process, distomesial margin unarmed; stylocerite directed slightly mesially in dorsal view and directed forward in lateral view, terminating in acute tooth, reaching tip of distolateral process of first segment, lateral margin strongly convex; second segment with blunt distolateral process; outer flagellum consisting of 12 articles. Antennal basicerite ( Figures 17B , 18A ) with rounded dorsodistal lateral angle; antenna scale 0.45 times as long as carapace, about 2.4 times longer than wide; lateral margin concave; distolateral tooth moderately slender, reaching distal margin of roundly triangular distal lamella.

Third maxilliped relatively slender; ultimate segment ( Figure 18C ) about 6.2 times longer than wide, penultimate segment about 2.6 times longer than wide; antepenultimate segment with pair of greatly unequal, movable spinules subdistally on ventral surface. First pereopod ( Figure 18D,E ) moderately stout; palm about 3.5 times longer than wide; carpus with small ventrolateral tooth; merus with small dorsodistal tooth. Fifth pereopod as illustrated ( Figure 18F ).

Uropodal exopod with minute posterolateral tooth and minute movable spinule just mesial to it ( Figure 18G ).

Colouration

Colour in life was described by Yaldwyn (1960).

Size

The non-ovigerous female holotype, CL 8.5 mm; the second female specimen is a spawning moult, CL 11.8 mm.

Distribution

Known only from the southern South Island, New Zealand, from type locality in Cook Strait and from the Wairarapa Seep, the Hikurangi Margin; 1007–1053 m.

Remarks

The present specimen, representing the second of this very rare species, agrees well with the holotype in every diagnostic aspect, and is the first record of the genus from a chemosynthetic environment.

As Yaldwyn (1960) noted, M. richardsoni is morphologically very similar to M. munita (Dana, 1851) from the northeastern Pacific. Komai (1995) pointed out that M. laevis (Yokoya, 1933) also shows substantial similarity to M. richardsoni . Differences among these three species were discussed in detail by Komai (1995).

Figures

Figure 17. Metacrangon richardsoni (Yaldwyn, 1960), female (CL 11.8 mm), NIWA 29392. (A) Carapace and cephalic appendages, lateral view; (B) same, dorsal view (setae partially omitted); (C) abdomen, lateral view; (D) first abdominal somite, dorsal view; (E) second to fourth abdominal somites, dorsal view; (F) fifth abdominal somite, dorsal view; (G) sixth abdominal somite and telson, dorsal view (tip of telson broken off). Scale bar: 5 mm.

Figure 18. Metacrangon richardsoni (Yaldwyn, 1960), female (CL 11.8 mm), NIWA 29392. (A) Rostrum, left eye and antennae, dorsal view; (B) left antennal scale, dorsal view (setae omitted); (C) distal two segments of left third maxilliped, ventral (flexor) view; (D) left first pereopod, lateral view; (E) same, subchela, dorsal (extensor) view; (F) left fifth pereopod (dactylus missing), lateral view; (G) posterolateral part of left uropodal exopod, dorsal view (setae omitted). Scale bars: 2 mm for C–F; 1 mm for A, B; 0.5 mm for G.