Serrata magna, 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 : 420-421

Serrata magna n. sp.

Figs 45-47, 61, 62

TYPE MATERIAL. — Holotype (lv) MNHN 20622 and 50 paratypes (lv and dd) MNHN 20623 , 2 (lv) paratypes MMM, 2 paratypes (lv) NMNZ.

TYPE LOCALITY. — Southern New Caledonia, 23°05’S, 167°45’E, 680-700 m [BIOCAL: stn DW 51] .

MATERIAL EXAMINED. — Southern New Caledonia. BIOCAL: Norfolk Ridge. BIOCAL: stn DW 70, 23°25’S, 167°53’E, 965 m, stn DW 48, 23°00’S, 167°29’E, 775 m, 39 dd (Figs 46, 47); stn 2 lv, 17 dd . — BATHUS 3: stn DW 809, 23°39’S, 167°59’E, 650- DW 49, 23°03’S, 167°32’E, 825-830 m, 2 dd; stn DW 51, 23°05’S, 730 m, 2 dd; stn DW 810, 23°40’S, 167°59’E, 850-900 m, 4 dd. 167°45’E, 680-700 m, 47 lv (holotype; Fig 45 and 38 paratypes — NORFOLK 1: stn DW 1689, Banc Eponge, 24°54’S, 168°23’E, MNHN, 2 MMM, 2 NMNZ), 76 dd (12 paratypes MNHN); stn 569-616 m, 9 dd, 15 fragments .

DW 53, 23°09’S, 167°43’E, 975-1005 m, 2 dd.

DISTRIBUTION. — Southern New Caledonia and northern Norfolk Ridge, live in 700-965 m, shells in 616-975 m.

DESCRIPTION. — Shell biconical, solid, opaque. Protoconch paucispiral, small, low, smooth. Spire high, massive, conical, whorls weakly convex. Aperture wide, oblique, widening slightly anteriorly. Base rather wide. Outer lip weakly thickened, slightly reflected in the centre, shoulder sloping, outer edge oblique, weakly convex anteriorly, outer margin narrow, thickened, rounded, not stepped, inner edge smooth, with long anterior part weakly excavated, posterior part shorter and more strongly excavated. Four thin columellar plaits, 2 anterior ones long, arched, very oblique, 2 posterior ones less oblique, decreasing in size posteriorly.

Ground colour whitish porcellaneous, sutural zone intense white.

Dimensions: 9.70 x 5.50 mm.

Radula from 5 specimens (Figs 61-62): uniserial, 24-26 plates 150 to 186 Μm wide, bearing 36-39 short unequal cusps, 1 out of 5 to 1 out of 8 being larger and thicker than the others.

REMARKS. — The shell morphology of Serrata magna is noticeably variable, from squat biconical to slender fusiform (Figs 45-47), with more or less convex spire whorls, a more or less oblique and reflected outer lip, and a more or less long, widened aperture. All intergrades are represented in the material examined and no tendency to differentiate into geographical forms can be recognised, even if shell shapes and sizes of local populations tend to be somewhat homogeneous. The length ranges from 7.90 to 10.70 mm. Serrata magna cannot be confused with any other Serrata species I have examined because of its large biconical shell with a wide aperture and a smooth, centrally reflected outer lip.

In the more inflated form of S. magna (Fig. 45), the outline is similar to that of S. perlucida (Fig. 33), except for the character of the outer lip. The less inflated and more biconical-fusiform forms of S. magna (Figs 46, 47) look roughly intermediate between S. hians (Figs 29, 30), S. tenuis (Fig. 36) and S. simplex (Fig. 52).

In many ways, the shell of S. magna is similar to that of several species of the Austroginella group, the decisive generic characters being its centrally reflected labrum and its comb-like radula with many subequal cusps, compared with the narrow chevron-shaped radula with a large, produced central cusp in the Austroginella group.

The range of S. magna , from 23°00’S to 24°54’S, includes all the northern Norfolk Ridge area in the mid-bathyal zone and appears to be wider than the ranges of most other Serrata species from New Caledonia.

ETYMOLOGY. — Latin magnus (adj., big, imposing), referring to the large size of the shell and to its imposing proportions.