Leptaxinus subovatus ( Jeffreys, 1881 )

Negri, Mauro Pietro & Corselli, Cesare, 2016, Bathyal Mollusca from the cold-water coral biotope of Santa Maria di Leuca (Apulian margin, southern Italy), Zootaxa 4186 (1), pp. 1-97 : 36

Leptaxinus subovatus ( Jeffreys, 1881)

Fig. 7 j–l

Axinus subovatus Jeffreys, 1881 (p. 704, pl. 61, fig. 8).

Axinulus subovatus ( Jeffreys, 1881) — Nordsieck 1969 (p. 80, pl. 13, fig. 48.13).

Leptaxinus (L.) subovatus (Jeffreys) — Di Geronimo 1974 (p. 156, pl. 3, fig. 2).

Thyasira (Parathyasira) subovata subovata ( Jeffreys, 1881) — Payne & Allen 1991 (p. 513, figs. 48–50, 53 a–b). Thyasira (Parathyasira) subovata minuta Payne & Allen 1991 (p. 515, figs. 51–52, 53 c–d). Thyasira (Parathyasira) subovata ( Jeffreys, 1881) — Giribet & Peñas 1997 (fig. 100). Thyasira subovata Jeffreys, 1881 — Oliver et al. 2002 (p. 60, pl. 25, figs. A–B).

Leptaxinus subovatus ( Jeffreys, 1881) — Repetto et al. 2005 (p. 310, bottom right fig.).

Diagnostic characters. Oval, oblique shell; long anterior side; roundly angular posterior side; outer surface with uneven and rather coarse growth markings; right valve hinge with 1 cardinal tubercle and 2 lamellar lateral teeth; left valve hinge with 1 cardinal tubercle. Prodissoconch: shell type ST-2D; length about 120 µm; roundish Dshaped outline; low convex profile; surface smooth; P-2 absent; transition to the nepioconch poorly marked.

Remarks. The specimens at hand appear to be more similar to the subspecies minuta Payne & Allen, 1991 , than to the nominal species of Jeffreys, in having an oval (not subtriangular) shell with rounded (not wedgeshaped) posterior angulation. We follow Oliver & Levin (2006) in preferring the genus Leptaxinus Verrill & Bush, 1898 for the present taxon, rather than Thyasira Lamarck, 1818 , for the presence of both cardinal tubercles and lateral teeth.

Occurrence. Box-corer samples BC10 (2 specimens), BC66 (2), BC67 (3), BC72 (5); cores BC21 (1), BC72 (5). Maximum length: 2.5 mm.

Distribution and habitat. Leptaxinus subovatus is distributed troughout the Atlantic, from Iceland and Faroes to Cape Verde, Angola and Argentina, and in the Mediterranean; it is found in the 200–4000 m bathymetric interval, reaching shallower depths at arctic latitudes ( Payne & Allen 1991; Poppe & Goto 1993; Di Geronimo et al. 2001; Sneli 2005).

Fossil record. Pliocene of northern Italy ( Tabanelli 2008).

Figures

FIGURE 7. a – c: Axinulus alleni (Carrozza, 1981); RV, sample BC 72, scale bars: 1 mm (a – b), 0.1 mm (c, prodissoconch); d – f: Thyasira flexuosa (Montagu, 1803); RV (e, f) and LV (d), sample BC 72, scale bars: 2 mm (d – e), 0.1 mm (f, prodissoconch); g – i: Genaxinus eumyarius (Sars M., 1870); RV (h, i) and LV (g), sample BC 72, scale bars: 1 mm (g – h), 0.1 mm (I, prodissoconch); j – l: Leptaxinus subovatus (Jeffreys, 1881); RV, sample BC 72, scale bars: 1 mm (j – k), 0.1 mm (l, prodissoconch); m – o: Mendicula ferruginosa (Forbes, 1844); RV, sample BC 72, scale bars: 1 mm (m – n), 0.1 mm (o, prodissoconch).