Serrata robusta, 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 : 419-420

Serrata robusta n. sp.

Figs 44, 48, 60

TYPE MATERIAL. — Holotype (lv) MNHN 20620 and 2 paratypes (dd) MNHN 20621 .

TYPE LOCALITY. — Southern New Caledonia, 22°59’S, 168°21’E, 500-504 m [SMIB 8: stn DW 201] .

MATERIAL EXAMINED. — Southern New Caledonia. SMIB 720, 22°52’S, 167°16’E, 530-541 m, 1 dd (Fig. 48) .

3: stn DW 21, 22°59’S, 167°19’E, 525 m, 1 dd. — SMIB 8: stn Norfolk Ridge. CHALCAL 2: stn DW 76, 23°41’S, 167°45’E, 470 DW 193-196, 22°59’S- 23°00’S, 168°21’E- 168°23’E, 491-558 m, m, 1 dd . — SMIB 8: stn DW 146-147, 24°55’S, 168°22’E, 508-532 17 lv, 18 dd; stn DW 201, 22°59’S, 168°21’E, 500-504 m, 1 lv m, 1 dd.

(holotype; Fig. 44) and 2 dd (paratypes). — BATHUS 2: stn DW

DISTRIBUTION. — Southern New Caledonia and northern Norfolk Ridge, live in 500-504, shells in 470-530 m.

DESCRIPTION. — Shell ovate-biconical, very solid, faintly translucent. Protoconch paucispiral, small, short, slightly angled, smooth. Spire tall, conical, whorls weakly convex. Aperture oblique, narrow posteriorly, noticeably widening over lower two thirds, narrowing strongly towards base. Base rather tapering. Outer lip thick, reflected over upper part, obliquely curved. Shoulder sloping, rounded, weakly delineated, outer edge arched, outer margin thickened, bevelled, not stepped, inner edge sinuous, noticeably excavated over anterior two thirds, bearing 13 short, closely packed denticles along most of its length, one much larger denticle bordering siphonal canal, smaller ones ranging along upper part of reflected zone of lip, upper part of inner margin smooth. Four rather prominent columellar plaits, lowest one oblique, sinuous, longer than others, second one oblique, rather straight, third one similar but less oblique, fourth one smallest, nearly horizontal, an inflated lump lies above fourth plait.

Ground colour porcellaneous white.

Dimensions: 6.90 x 3.70 mm.

Radula from 1 specimen (Fig. 60): uniserial, 22 plates about 208 Μm in width, bearing about 36 triangular cusps, about 1 out of 5 being larger than others. Smaller cusps in intervals between larger ones make a concave series. General outline of plate weakly convex.

REMARKS. — The shell morphology of Serrata robusta is constant throughout its wide distribution, from 22°52’S to 24°55’S. Its principal variability is in shell length (4.90-7.80 mm), relative spire length, and thickness of the shell, without a visible geographical cline (Figs 44, 48). Serrata robusta differs from the other Serrata species from New Caledonia mainly in its thick, arched outer lip with a sinuous inner edge bearing well-defined subequal denticles and a distinctive larger denticle bordering the siphonal canal, combined with a narrowed siphonal canal, a truncated base, an oval-biconical outline with a produced spire, and four thick columellar plaits continued by an inflated lump.

The depth at all 6 collecting stations was quite similar.

ETYMOLOGY. — Latin robustus (adj., robust), referring to the strong, solid aspect of the shell.