Otitoma carnicolor

Otitoma carnicolor (Hervier, 1896)

Fig. 1 M–S

Drillia carnicolor Hervier, 1896: 141. Type locality: Lifu Island.

Material examined

LOYALTY ISLANDS: 2 spms (1 juv), Atelier LIFOU, Stn 1444, Lifou, Santal Bay, NE of Gaatcha Bay, 20°55.0 ′ S, 167°05.2 ′ E, 9–20 m; 2 spms, Atelier LIFOU, Stn 1432, Lifou, Santal Bay, Récif Shelter, 20°53.5 ′ S, 167°02.7 ′ E, 12–32 m; 1 spm (eroded), Atelier LIFOU, Stn 1438, Lifou, Santal Bay, Chépénéhé Point, 20°47.7 ′ S, 167°09.35 ′ E, 16 m.

Description

Shell claviform-fusiform (b/l 0.36–0.37; a/l 0.44–0.50), somewhat pupoid. Teleoconch of 4½–4¾ weakly and evenly convex whorls with periphery just below mid-whorl height on earlier two whorls, at mid-whorl on later ones. Suture shallow, bordered by a sub-sutural fold, demarcated by a shallowly concave sutural ramp. Axial ribs opisthocline and rounded, equal in width to or wider than intercostal space, extend from whorl base to sub-sutural fold but becoming rather weak on sutural ramp. 12–13 axial ribs on penultimate whorl, 12–16 on last whorl. Spiral sculpture (Fig. 1P) of narrow, widely-spaced spiral cords, not forming distinct nodules where crossing axial ribs. First two teleoconch whorls with a sub-sutural cord, 1–2 weak cords (abapical one stronger) on sutural ramp and two main cords below ramp, 1–2 additional main cords develop on subsequent two whorls. Last whorl with 8–9 spiral cords on base and rostrum. Interspaces between spiral cords sculptured by dense, closely-spaced fine spiral threads irregularly plicate by axial incremental lines. Aperture rather narrow, slightly constricted at entrance to siphonal canal, the latter short, slightly expanded terminally, somewhat obliquely truncated. Inner lip with moderately thick callus and strong parietal pad. Outer lip edge sharp, preceded by a wide, low, rounded varix. Stromboid notch distinct. Anal sinus moderately deep, U-shaped, with strongly constricted opening. Protoconch papilliform, of 1½ whorls, superficially smooth but under SEM with traces of somewhat spirally-aligned granules (Fig. 1 R–S). Protoconch diameter 0.90–0.95 mm. Dimensions (based on two well preserved adult specimens): 7.3 × 2.6 mm, aperture height 3.2 mm (Stn 1444); 6.45 × 2.4 mm, aperture height 3.25 mm (Stn 1432). Color pale-yellowish.

Remarks

This species was originally described from Lifou Island and cited by Bouge & Dautzenberg (1914). It has subsequently been ignored until Kilburn (2004) included it in his list of Otitoma species. The available material positively compares with the photographs of the syntypes of Drillia carnicolor published by MNHN (https://science.mnhn.fr/institution/mnhn/collection/im/item/ 2000-2863) and is accordingly considered conspecific. Wiedrick (2014) assigned Drillia carnicolor to Thelecytharella, even though the species clearly resembles an unidentified species from the Philippines, which the author assigned to Otitoma (Wiedrick 2014: 53, figs 10–12). Actually, Otitoma carnicolor resembles O. cyclophora in type of protoconch structure and interstitial sculpture of numerous spiral threads (Fig. 1Q) but otherwise differs distinctly mainly in its smaller size (6.45–7.3 mm vs 10.9– 7.7 mm), larger protoconch (0.90– 0.95 mm vs 0.52–0.59 mm) and very different axial ribbing. In particular, O. cyclophora has more numerous and weaker axial ribs, which become distinctly arcuate on the sutural ramp, while in O. carnicolor the axial ribs are stronger and straight. Furthermore, O. carnicolor has a shallower anal sinus compared to that of O. cyclophora. Under SEM the protoconch surface of O. cyclophora is seen to be covered by somewhat spirally-aligned granules (Fig. 1L). Traces of similar microscopic granules are also seen on the partially abraded protoconch surface of O. carnicolor.