Serrata hians, Boyer, 2008

Boyer, Franck, 2008, The genus Serrata Jousseaume, 1875 (Caenogastropoda: Marginellidae) in New Caledonia, Mémoires du Muséum national d'Histoire naturelle 196, pp. 389-436 : 409-410

Serrata hians n. sp.

Figs 29-31

TYPE MATERIAL. — Holotype (dd) MNHN 20610 and 20 paratypes (dd) MNHN 20611 , 2 paratypes (dd) MMM, 2 paratypes (dd) NMNZ.

TYPE LOCALITY. — Norfolk Ridge , 23°33’S, 167°16’E, 550-570 m [BERYX 11: stn DW 35] .

MATERIAL EXAMINED. — Southern New Caledonia. BIOCAL: Norfolk Ridge. BERYX 11: stn DW 35, 23°33’S, 167°16’E, 550- stn DW 33, 23°10’S, 167°10’E, 675-680 m, 1 dd, 1 lv (Fig. 31) 570 m, 48 dd (holotype, Fig. 29 and 20 paratypes MNHN, 2 as S. cf. hians n. sp; stn DW 36, 23°09’S, 167°11’E, 650-680 m, MMM, 2 NMNZ); stn CH 41, 23°39’S, 168°00’E, 230-360 m, 3 dd (Fig. 30). 4 dd .

DISTRIBUTION. — Southern New Caledonia and northern Norfolk Ridge, live in 675-680 m, shells in 360-675 m.

DESCRIPTION. — Shell slender oval, solid, opaque. Protoconch paucispiral, small, slightly bulging, smooth. Spire slender conical, pointed, whorls flat. Aperture widening markedly towards anterior. Base rather wide. Outer lip moderately thickened in centre, attenuated towards base. Shoulder sloping, short, outer edge slightly arched, outer margin moderately thickened, bevelled, slightly stepped, inner edge subvertical in central and posterior areas, bearing 1 strong button-like denticle on side of siphonal canal and 12 small, sharp denticles spread lower, much smaller than the interspaces. Four thin columellar plaits, 2 anterior ones oblique, weakly sinuous, 2 upper ones less oblique, decreasing in size posteriorly.

Ground colour whitish porcellaneous.

Dimensions: 8.50 x 4.00 mm.

Radula unknown.

REMARKS. — The shell morphology of Serrata hians is not very variable over its limited range (23°09’S to 23°39’S). Some shells are slightly more slender than the holotype, with slightly more prominent labial denticles or a very small pleat just above the uppermost columellar plait, the other characters remaining constant (Fig. 30). The length ranges from 7.70 to 9.85 mm. A closely matching specimen, having a stouter spire with more convex sides and a wider aperture, is figured as Serrata cf. hians (Fig. 31). This specimen was collected at station DW 33 together with a shell with features typical of S. hians .

Two shells from the present type material were erroneously attributed by Boyer (2001) to the much smaller species Serrata [as Haloginella ] boucheti Boyer, 2001 , which is restricted to one seamount on the northern Norfolk Ridge.

Serrata hians is regarded as the typical species of a group of Serrata species occurring off southern and southeastern New Caledonia and on the Norfolk Ridge. The common characters defining this group are a medium-sized shell with a moderately to markedly widened aperture, thin columellar plaits arranged in a fan-like (radiating) pattern, and a rather thin to very thin labrum with no denticles or very small ones. The shells of fresh specimens are not decorated and have a uniform whitish porcellaneous to vitreous white ground colour. The single radula known in this group is a classic comb-like radula bearing a notably high number of subequal cusps.

The species included in the S. hians species group that occur in the Norfolk Ridge area seem to be found mainly at mid-bathyal depths (570-1070 m, except for 1 station with S. hians at 360 m).

ETYMOLOGY. — Latin hians (adj., yawning), referring to the widely opened aperture of the shell.