Clavus unizonalis (Lamarck, 1822)

(Figs. 6 A–I, 7 A, B)

Pleurotoma unizonalis Lamarck 1822: 92 .

Pleurotoma vidua Reeve 1845: pl. 22, sp. 19.

Drillia vidualoides Garrett 1873: 217, pl. 2, fig. 28.

Pleurotoma (Clavus) nigrozonatus Weinkauff 1876: 60, pl. 13, fig. 2. [Proposed as a substitute name for Pleurotoma vidua Reeve, 1845 non Pleurotoma vidua “ Hinds” [sic]].

Other references

Pleurotoma unizonalis; Kiener 1840: 54, pl. 22, fig. 2; Reeve 1843: pl. 13, fig. 113.

Clavus unizonalis; Powell 1966: 71; Cernohorsky 1972: 186, pl. 53, fig. 14; Kilburn 1988: 182, figs. 5, 8, 75–77; Wells 1991: 24, pl. 1, figs. 2 (radula), 4 (operculum); pl. 5, figs. 8–9, 10 (holotype); pl. 6, figs. 1–2 (syntype P. vidua); Taylor et al. 1993: fig. 16 c (radula), 25 (diagram of foregut); Wilson 1994: 184, pl. 40, fig. 3; Sysoev in Poppe 2008: pl. 674, figs. 3–4.

Clavus (Tylotia) unizonalis; Hasegawa et al. 2000: 621, pl. 309, fig. 10.

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

Clavus viduus [sic]; Cernohorsky 1978: 152, pl. 54, fig. 7a (not 7); Higo et al. 1999: 298; Higo et al. 2001: 100, fig. G3454 (syntype); Sysoev in Poppe 2008: pl. 674, figs. 6–7.

Drillia vidualoides; Melvill & Standen 1897: 397; Bouge & Dautzenberg 1914: 143.

Clavus vidua var. vidualoides; Hedley 1922: 257, pl. 45, fig. 51 (operculum).

Clavus bilineatus; Sysoev in Poppe 2008: pl. 673, figs. 2–3 only (non Reeve, 1845).

Type data. Pleurotoma unizonalis: holotype MHNG 1097/55, type locality unknown. Pleurotoma vidua ( P. nigrozonatus): 3 syntypes NHMUK 1966435; type locality: Island of Masbate, Philippines, found at low water. Drillia vidualoides: 3 syntypes ANSP 15324; type locality: Viti Is. [Fiji].

New caledonian material examined (total 14 lots, 26 spms):

New Caledonia, EXPÉDITION MONTROUZIER, Koumac, Stn. 1303 (1 spm); Touho Stns. 1240 (5 spms), 1241 (1 spm), 1242 (20 spm), 1245 (3 spms), 1246 (1 spm) 1248 (1 spm);

Loyalty Islands, PLOUVEAL, Stns. 1222 (1 spm), 1232 (2 spms);

Lifou, LIFOU 2000, Stns. 1407 (1 spm), 1419 (1 spm), 1424 (1 spm), 1426 (3 spms);

Loyalty Ridge, MUSORSTOM 6, Stn. DW430 (2 spms).

Distribution. Mozambique and Western Australia to Papua New Guinea, Philippines and Okinawa, and across Pacific to Fiji and New Caledonia, intertidal to 30 m, in coarse sand, stones and sediment, on reefs and among algae, in our material confirmed alive to ca 15 m.

Description. Shell thick, claviform, adult length to 26 mm, breadth/length 0.31–0.47, aperture/total length 0.35–0.46); suture somewhat crenulate, deeply recessed anteriorly, adpressed to previous whorl; base broad, shallowly indented, fasciole distinct in adult shells. Outer lip with crenulate edge, anal sinus a widely open “U”, parietal tubercle large; stromboid notch distinct. No subsutural cord or sulcus. Terminal varix slightly behind lip. Axial ribs opisthocline, very feeble on subsutural slope and at parietal level, projecting at periphery on last whorl, in unworn or immature shells angular and slightly squamiform, 8–12 on penultimate whorl. Spiral sculpture of 8–11 coarse, declivous ridges on fasciole; lower part of last whorl at parietal level with 2–3 rows on nodules on secondary radial riblets; surface covered with dense, rather rugose, microscopic spiral threads, and coarser collabral ones.

Subsutural region and periphery of ribs white to pale grey, last whorl with a broad, dark reddish- to blackishbrown band, usually showing above suture on spire whorls, base often but not always paler or even white, basal nodules (when present) white; inner lip brown, external brown band showing through to interior.

Protoconch (Fig. 6 I) worn in most material seen, in single studied specimen narrow, of about two smooth (except row of micropustules along suture) moderately convex whorls, diameter ca 600 Μm, height about 570 Μm. Protoconch-teleoconch transition indistinct, marked by appearance of anal sinus.

Measurements (adult New Caledonian examples): 22.1 x 8.9 mm, 20.2 x 6.2 mm; 20.1 x 8.2 mm; 18.9 x 7.2 mm; 20.2 x 8.5 mm.

Radula. (Fig. 7 A, B): Rachidian narrow, slightly notched anteriorly, with strong median cusp and fine side denticles. Lateral teeth broad, arcuate, with 17 cusps, 4th–6th from inner side being the longest and gradually diminishing in length towards outer side, where they evanesce. Marginal teeth rather long and narrow, with broader short blade, about 1/3 of teeth length. Blade edges slightly thickened. Accessory limb weak. About 45 rows of teeth.

Radula also illustrated by Kilburn (1988) and Wells (1991).

Remarks. Several workers, most recently Wells (1991), have synonymised Pleurotoma vidua with P. unizonalis, whereas others (e.g. Higo et al. (1999), Cernohorsky (1972 and 1978)) maintain them as distinct. Although typical examples of each are usually easily distinguishable, we find a precise diagnosis of their differences to be so elusive, that we must concur in recognizing only one variable species. It is possible that extensive series will reveal a geographical basis for shell characters—with typical unizonalis more characteristic of the Indian Ocean east to Indonesia and Papua New Guinea, and vidua of the western Pacific from the Philippines to Fiji—but this is largely speculative. None of the material examined from New Caledonia is referable to typical C. unizonalis . The nominal forms are briefly defined below:

Pleurotoma vidua: Typical examples appear to differ from Clavus unizonalis in their somewhat higher spire (the widest part of the shell being anterior to median, not more or less median), the presence of 8–12 stronger ribs (7–8 more rounded ribs in unizonalis), the more angular whorl periphery and the entire base of the last whorl being brown (typical unizonalis is white with a discrete brown to black median band on the last whorl), usually with 1–4 rows of white basal granules (present in approximately 0.4 of the available adult New Caledonian material). Incidentally, by his choice of vernacular name, Reeve made it clear that the specific name was derived from the Latin noun “ vidua ” (“a widow”), not the adjective “ viduus ” (“bereft”).

Pleurotoma (Clavus) nigrozonatus: As pointed out by several early authors, this name was proposed in the mistaken belief that Reeve’s Pleurotoma vidua had already been utilized by Hinds. The figure reference to Hinds’ work, given by Weinkauff as “pl. 6, fig. 6”, actually illustrates Clavatula [= Lienardia] rubida Hinds, 1843, and the cited text reference (“p. 60”) contains no mention of vidua or any other turrid name.

Drillia vidualoides: This was said by Garrett to differ from his concept of “ Drillia vidua ” in its blunter nodules, non-whitish base and the lack of granules on the base. Curiously, all three specimens in the ANSP collection labelled as syntypes are a good deal larger than the 10 mm given by Garrett (viz. 23.7 x 10.2 mm, 18.0 x 7.7 mm and 18.8 x 7.9 mm). However, one may assume a lapsus calami, as Garrett’s figure, which is not accompanied by a scale bar and is presumably life-sized, measures ca 23 mm. It is not the similar-sized individual listed above, as that has the white basal granules considered characteristic of C. vidua by Garrett (as does the 18.8 mm juvenile). The only one of the three to agree in lacking these granules, and in its rounded axial ribs, is the somewhat worn specimen.

The only character that might be used to distinguish vidualoides from the vidua form of C. unizonalis is the lack of an angle to the axial ribs (the brown base originally considered diagnostic occurs also in syntypes of vidua). A few examples from the present expeditions e.g. Touho Stns. 1245 (fig. 6 E, F) and 1240 are typical of vidualoides, but others appear intermediate.