Clavus exasperatus (Reeve, 1843)

Kilburn, Richard N., Fedosov, Alexander & Kantor, Yuri, 2014, The shallow-water New Caledonia Drilliidae of genus Clavus Montfort, 1810 (Mollusca: Gastropoda: Conoidea), Zootaxa 3818 (1), pp. 1-69 : 12-14

Clavus exasperatus (Reeve, 1843)

( Figs. 2 E, F, 4 A–H)

Pleurotoma exasperata Reeve 1843 : pl. 2, sp. 8; Weinkauff 1876: 54, pl. 12, figs. 1, 3.

Pleurotoma exigua Hombron & Jacquinot 1848: 111 , pl. 25, figs. 21–22 (date of publication fixed by the Atlas , provided here after Clark & Crosnier 2000).

Other references.

Clavus exasperatus ; Hedley 1922: 257, pl. 45, fig. 50 (protoconch); Wells 1991: 11, pl. 1, figs. 1 (radula), 3 (operculum); pl. 3, figs. 3–4 (as possible syntype); Wilson 1994: 184, pl. 40, figs. 2, 5; Higo et al. 2001: 100, fig. G3542 (holotype).

Austroclavus exasperatus ; Cotton 1947: 12.

Drillia (Clavus) auriculifera var. exasperata ; Bouge & Dautzenberg 1914: 136.

Clavus (Tylotia) exaperatus [sic]; Hasegawa et al. 2000: 621, pl. 309, fig. 8.

Clavus exasperatus ; Sysoev in Poppe 2008: pl. 673, fig. 5 only (not fig. 4).

Type data. P. exasperata : probable holotype NHMUK 1966462 (figured as “HT” [“ holotype ”] by Higo et al. 2001), type locality unknown. P. exigua : lost ( Wells 1991), type locality: Torres Straits, Queensland.

New caledonian material examined (total 14 lots, 14 spms):

New Caledonia, LAGON, Stns. 342 (1 spm), 487 (1 spm), 1139 (1 spm);

EXPÉDITION MONTROUZIER, Touho Stns. 1268 (1 spm), 1272 (1 spm).

Loyalty Islands, Lifou: LIFOU 2000, Stns. 1420 (1 spm), 1422 (1 spm), 1423 (1 spm), 1424 (1 spm), 1428 (1 spm), 1433 (1 spm), 1447 (1 spm), 1451 (1 spm), 1457 (1 spm).

Distribution. Japan and Hawaii to New Caledonia, Loyalty Islands and Solomon Islands, west to Djibouti, Mauritius and southern Mozambique, in sand or stones under and between dead coral, low tide to about 31 m (elsewhere to 75 m).

Description (New Caledonian population): Shell thick, broadly claviform (breadth/length 0.45–0.49) with sharp, initially coeloconoid spire, apex often somewhat stiliform; suture between later whorls fissure-like (partly recessed under edge of succeeding whorl); fasciole strong, with distinct false umbilicus; aperture oblong-ovate, aperture/total length 0.40–0.47), outer lip slightly alate, base wide, oblique, shallowly indented. Outer lip slightly prosocline, gently curved, strongly serrated, stromboid notch very deep, anal sinus U-shaped, directed slightly adapically, parietal pad forming a large tubercle; base of columella curved to right, forming a small, often sharp basal projection.

First 2–3 whorls rather flat-sided, with suture-to-suture axial ribs; thereafter, the latter become progressively weaker subsuturally and more tumid basally. Later whorls with subsutural region rising high up preceding whorl, flattened, becoming concave above shoulder; shoulder sometimes defined by a low ridge with sharply incised adapical edge, which bears a series of nodules that similarly terminate abruptly above at border of sulcus; in others they are evenly rounded; on latter part of last whorl the nodules occasionally form secondary extensions that cross to suture. Nodules rounded or squamiform (often in same individual), 12–14 on penultimate whorl, in t/s angularly rounded or rounded-angular to spathulate (when strongly squamiform), with sloping sides, mostly subequal to intervals, base of nodules rapidly evanescing above last suture. Early whorls with seven straight, almost orthocline ribs per whorl. Varix moderately strong, roundly angular, shouldered posteriorly, evanescing anteriorly. Base of last whorl with a series of faint spirally arranged bumps, strengthening towards back of lip into 3–7 rows of low nodules; rostrum with 7–9 rounded spiral ridges. Entire surface covered with dense, wavy microscopic spiral striae, collabral threads coarser and irregular.

Uniform greyish- or yellowish-white, sometimes with a broad, faint band of pale buff around middle of last whorl; columella and lip white, interior of aperture yellowish; apical whorls evidently brown.

Protoconch rounded conical, somewhat cylindrical, of two smooth whorls, diameter about 660 Μm (one example only).

Measurements. 26.6 x 13.9 mm (largest adult); 24.7 x 11.7 mm (smallest adult).

Radula ( Fig. 2 E, F): Rachidian very broad, width exceeding length, shallowly notched anteriorly, with strong median cusp and fine side denticles. Lateral teeth broad, arcuate, with 16–17 cusps, 2nd–5th from inner side being the longest and gradually diminishing in length towards outer side, where they evanesce. Marginal teeth rather long, with poorly pronounced short blade, about 1/5 of teeth length. Accessory limb absent. About 35 rows of teeth.

Remarks. As was observed by Wells (1991), Clavus exasperatus shows a certain amount of geographical variation. The New Caledonian population, although characteristic, is not here recognised as taxonomically distinct, although a full description of this material is given above. Typical New Caledonian individuals differ from typical examples of C. exasperatus (the probable holotype in the NHMUK most closely resembles the Indian Ocean population) in having peripheral nodules that are sharply cut adapically and are usually more or less squamiform, a base that lacks axial sculpture and is completely smooth in immature shells (in exasperatus it bears the tapering bases of the axial ribs, usually with vermiculate threads interpolated). Nevertheless, apparently intermediate individuals also occur in New Caledonia: these have rounded peripheral tubercles, and axial ribs with basal extensions and weak interpolated riblets. New Caledonian individuals are always off-white except sometimes for a faint buff zone, never dark brown or with streaks of brown as in the type and similar specimens from other parts of Indo-West Pacific, and the tooth-like base to the columella callus is absent or indistinct in the latter.

Figures

FIGURE 2. Radulae of Clavus canalicularis, C. exasperatus and C. boucheti. A – D. Clavus canalicularis A, B. EXPÉDITION MONTROUZIER, Koumac, Stn. 1277, SL 30.5 mm; C, D. LAGON, Nouméa Sector, Stn. 289, SL 22.8 mm (shell—Fig. 1 H); E, F. Clavus exasperatus, Loyalty Islands, Lifou, LIFOU 2000, Stn. 1420, SL 25.9 mm (shell—Fig. 4 H); G, H. Clavus boucheti, New Caledonia, LAGON, Grand Recif Sud, Stn. 305, SL 24.5 mm (shell—Fig. 5 F).