Hadroconus scobina, Herbert, 2024

Herbert, David G., 2024, The Vetigastropoda (Mollusca) of Walters Shoal, with descriptions of two new genera and thirty new species, European Journal of Taxonomy 923, pp. 1-119 : 44-46

Hadroconus scobina sp. nov.

urn:lsid:zoobank.org:act:D5D500E3-1B96-4A37-BCA4-70D5544D363F

Figs 18D–H , 19C–D

Diagnosis

Shell trochiform, spire weakly coeloconoid, periphery with flange-like keel; early sculpture of distinct, evenly spaced, sinuous axial riblets, with a strong spiral cord at shoulder; additional finer spiral cords and lirae developing below shoulder cord; sculpture generally weak on last adult whorl; base with 2–5 distinct subperipheral spiral cords; umbilicus moderately broad; outer lip with a deep U-shaped posterior sinus, a distinct labral projection, a second shallower sinus below periphery, and a third small sinus at base of columella; interior with low collabral thickening extending from insertion of outer lip.

Etymology

From the Latin “ scobina ” – “a file” (noun in apposition); in reference to the file-like sculpture of the spire whorls.

Material examined

Holotype

WALTERS SHOAL • empty shell; slopes, stn DW4885; 33°17′ S, 43°55′ E; depth 272–380 m; 3 May 2017; MNHN-IM-2000-38060 .

Paratypes

WALTERS SHOAL – slopes • 3 empty shells; same collection data as for holotype; MNHN- IM-2000-38061 • 5 empty shells; stn DW4892; 33°12′ S, 44°01′ E; depth 624–646 m; 4 May 2017; MNHN-IM-2000-38062 • 12 empty shells; stn DW4898; 33°09′ S, 44°01′ E; depth 652–668 m; 6 May 2017; MNHN-IM-2000-38063 • 3 empty shells; stn DW4899; 33°09′ S, 44°02′ E; depth 707–720 m; 6 May 2017; MNHN-IM-2000-38064 • 9 empty shells; stn DW4900; 33°10′ S, 44°01′ E; depth 660– 670 m; 6 May 2017; SEM shell; MNHN-IM-2000-38065 .

Other material

WALTERS SHOAL – slopes • 2 empty shells; stn CP4901; 33°09′ S, 44°01′ E; depth 647–672 m; 6 May 2017; MNHN • 2 empty shells; stn CP4902; 33°08′ S, 44°02′ E; depth 700–711 m; 7 May 2017; MNHN • 1 empty shell, juvenile; stn CP4906; 33°26′ S, 44°00′ E; depth 799–837 m; 9 May 2017; MNHN • 8 empty shells; stn DW4877; 33°10′ S, 43°49′ E; depth 217–256 m; 1 May 2017; MNHN • 3 empty shells; stn DW4886; 33°17′ S, 43°56′ E; depth 573–582 m; 3 May 2017; MNHN • 12 empty shells; stn DW4887; 33°17′ S, 43°57′ E; depth 599–640 m; 3 May 2017; MNHN • 1 empty shell; stn DW4890; 33°09′ S, 43°59′ E; depth 492–588 m; 4 May 2017; MNHN • 14 empty shells; stn DW4892; 33°12′ S, 44°01′ E; depth 624–646 m; 4 May 2017; MNHN • 50+ empty shells; stn DW4898; 33°09′ S, 44°01′ E; depth 652–668 m; 6 May 2017; MNHN • 16 empty shells; stn DW4899; 33°09′ S, 44°02′ E; depth 707–720 m; 6 May 2017; MNHN • 27 empty shells; stn DW4900; 33°10′ S, 44°01′ E; depth 660–670 m; 6 May 2017; MNHN .

Description

SHELL. Small, trochiform (diameter up to 4.3 mm), wider than high (H/D =0.67–0.75); spire weakly coeloconoid, whorls convex, suture shallowly to moderately indented, periphery angular with flange-like keel; spire whorls strongly sculptured, last adult whorl weakly so; base somewhat flattened, with moderately wide umbilicus; teleoconch of up to 5.5 whorls. First teleoconch whorl with a strong spiral cord midway between sutures (P1, shoulder cord), another (P2) at whorl periphery, level with or just above abapical suture ( Fig. 19D ); distinct axial sculpture of evenly spaced riblets (30–32) extending from suture to suture; riblets initially collabral, becoming sinuous above P1 toward end of whorl; sculpture of whorls 2–4 similar to that on first whorl, but with 2–3 additional finer spiral cords developing below P1 ( Fig. 19C ); P2 strengthening and becoming keel-like; P1 no longer prominent on fifth whorl, additional fine spiral lirae develop above periphery; axial sculpture weakens toward end of fifth whorl, sometimes evident only as faint growth-lines; spiral sculpture variable on latter part of final whorl, scarcely visible in some individuals but fine, close-set lirae present in others; periphery angular, delineated by flange-like keel. Base with 2–5 distinct subperipheral spiral cords, but basal spiral sculpture weakening toward umbilicus and appearing as fine incised lirae; umbilicus with steep sides; umbilical margin a low rounded cord, rather indistinct. Aperture obliquely quadrate; outer lip with a deep U-shaped posterior sinus, its edge flaring outward; below this a distinct labral projection (corresponding with a shallow indentation in whorl profile in some individuals); a second shallower sinus below periphery, its edge flaring; a third small sinus at base of columella; columella more or less straight, distinctly oblique and with a somewhat thickened and reflected margin; angle between columella and paries acute; interior of outer lip with low prosocline thickening extending from its insertion on penultimate whorl, lip thin and fragile beyond this.

PROTOCONCH ( Fig. 19D ). White; diameter 235–250 μm, comprising ca 1.25 whorls, apical bulb evenly rounded; mostly smooth, but with traces of superficial granulation near apex; terminal lip almost straight or weakly convex, not conspicuously thickened.

COLOUR. Uniformly milky-white, somewhat translucent; interior faintly nacreous.

DIMENSIONS. Holotype, height 2.8 mm, diameter 3.7 mm; largest specimen, height 2.9 mm, diameter 4.3 mm.

Distribution

Known only from the slopes of Walters Shoal, at depths of 256–799 m; on coarse sandy substrata with diverse cnidarians, molluscs, crustaceans and ophiuroids; living specimens unknown.

Remarks

Hadroconus scobina sp. nov. is smaller and comprises fewer whorls than its congeners. Many of the more than 100 specimens available exhibit a mature outer lip profile indicating cessation of growth, but none exceeds a diameter of 4.3 mm or has more than 5.5 whorls. In addition, the protoconch is substantially smaller than in the other species for which this is known (diameter ≤ 250 μm vs ≥ 375 μm). It also differs from other species of Hadroconus in having more convex whorls, a more distinctly coeloconoid profile, finer sculpture and a much less clearly demarcated umbilical margin.

Hadroconus sibogae ( Schepman, 1908) from Indonesia has coarser axial riblets which crenulate the peripheral keel, and the umbilicus is bordered by a strongly beaded rib. Hadroconus diadematus Marshall, 1988 from New Zealand has a distinct angular suprasutural cord above which are numerous fine spiral threads and it retains well-defined sculpture on the last adult whorl. Hadroconus grandiosus Marshall, 1991 from south of New Caledonia has flatter whorls without any sutural indentation and also has an angular suprasutural cord, though not as strong as that of H. diadematus . Hadroconus altus (Watson, 1879) from the Caribbean has an evenly trochoid profile and the peripheral carina is rendered crenate by the relatively coarse axial riblets.

As in H. altus (cf. Quinn 1987), intraspecific variation in shell morphology in H. scobina sp. nov. is considerable, both in terms of shell shape and strength of sculpture. In some specimens the last adult whorl becomes progressively more flattened below the adapical suture ( Fig. 18H ), resulting in an almost tabulate shoulder region in the final half-whorl. Likewise, although the axial riblets of the spire whorls are weak or scarcely evident on the final whorl in nearly all specimens, the strength of the spiral sculpture on the last adult whorl varies considerably, being confined to the supra-peripheral region in some individuals, but covering much of the adapical surface in others. The extent of intraspecific variation in the remaining species of Hadroconus is unknown since they are known from very few specimens.

Figures

Fig. 18. A–C. Fluxinella dufresneae sp. nov., holotype, diameter 6.0 mm (MNHN-IM-2013-67291). D–F. Hadroconusscobinasp. nov.,holotype, diameter3.7mm (MNHN-IM-2000-38060).G. Hadroconus scobina sp. nov., holotype, SEM (uncoated) to show detail of sculpture. H. Hadroconus scobina sp. nov., specimen with shouldered whorls, diameter 4.0 mm, stn DW4898 (paratype, MNHN-IM-2000-38063).

Fig. 19. A–B. Fluxinella dufresneae sp. nov., juvenile paratype (MNHN-IM-2000-38058). A. Spire whorls. B. Protoconch. C–D. Hadroconus scobina sp. nov., paratype (MNHN-IM-2000-38065). C. Oblique view of spire whorls. D. Protoconch. E–J. Seguenzia cf. S. emmeles Marshall, 1991, Walters Shoal, stn CP4913, height 1.63 mm, diameter 1.50 mm (MNHN). E–G. Apertural, oblique basal and apical views of shell. H. Detail of sculpture showing more numerous axial riblets below shoulder keel. I. Side view of apex. J. Protoconch. Scale bars: A, C = 0.5 mm; B, D, J = 100 μm; E–G = 1.0 mm; H–I = 200 μm.