Serrata perlucida, 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 : 411-412

Serrata perlucida n. sp.

Figs 33, 64

TYPE MATERIAL. — Holotype (lv) MNHN 20613 and 1 paratype (lv) MNHN 20614 .

TYPE LOCALITY. — Norfolk Ridge , 24°11’S, 167°32’E, 1070 m [BIOCAL: stn CP 61] .

MATERIAL EXAMINED. — Norfolk Ridge. BIOCAL: stn CP 61, 24°11’S, 167°32’E, 1070 m, 2 lv (holotype, Fig. 33 and paratype) ;

stn DW 70, 23°25’S, 167°53’E, 965 m, 2 lv.

DISTRIBUTION. — Northern Norfolk Ridge , live in 965-1070 m .

DESCRIPTION. — Shell inflated, very thin, subtranslucent. Protoconch paucispiral, wide, dome-shaped, smooth. Spire high, massive, conical, stepped, whorls strongly convex, suture incised, subcarinate. Aperture very wide, oblique, widening slightly towards base. Base wide. Outer lip very thin, arched, straightening slightly in central part, shoulder sloping, rounded, outer margin very narrow, slightly rounded, stepped, inner edge smooth. Four thin, oblique columellar plaits, lower one long, subvertical, slightly angled over anterior part, 3 upper plaits decreasing in size posteriorly.

Ground colour whitish hyalinous-vitreous, narrow subsutural zone intense white.

Dimensions: 6.90 x 3.35 mm.

Radula from 1 specimen (Fig. 64): uniserial, 24 plates around 121 Μm in width, bearing 48 short, subequal, pointed cusps.

REMARKS. — Despite its juvenile appearance, Serrata perlucida has a perfectly mature labrum with a stepped and well-marked margin. In its very thin, inflated, juvenile-looking shell, its very wide aperture, its sharp outer lip with a smooth inner edge, its stepped spire with convex whorls, and its very thin plaits, S. perlucida differs markedly from the other Serrata species known from New Caledonia. However, as demonstrated below, its shell belongs to a morphological sequence of species from the mid-bathyal zone linking it to the genus Serrata . Its radula is also typical of the genus (Fig. 64), and it is similar to those of S. fasciata from New Zealand (Fig. 55) and S. translata from the Society Islands (Fig. 56) in the high number of subequal cusps.

The geographical range of S. perlucida is known to be from 23°25’S to 24°11’S, but the species is apparently restricted to quite deep water at around 1000 m, where very few samples have been collected. So, the range of S. perlucida might actually be considerably wider than the available data indicate.

As far as the shell morphology is concerned, S. perlucida is linked to S. hians by the way of the intermediate species described below. Serrata perlucida has the same thin, fan-like arrangement of columellar plaits as S. hians , together with a wide aperture and a thin labrum, but has a thinner and more hyalinous shell with a stouter outline and a wider spire, a much wider aperture and a much thinner and sharper outer lip.

ETYMOLOGY. — Latin perlucida (adj., transparent), referring to the hyaline transparency of the shell.