Provanna hirokoae, Amano & Little, 2014

Amano, Kazutaka & Little, Crispin T. S., 2014, Miocene abyssochrysoid gastropod Provanna from Japanese seep and whale-fall sites, Acta Palaeontologica Polonica 59 (1), pp. 163-172 : 164-166

Provanna hirokoae sp. nov.

Fig. 2 .

2010 Provanna sp. ; Amano et al. 2010: figs. 5C–E.

Etymology: Named for the first author’s wife Hiroko.

Type material: Holotype, JUE 15901 ( Fig. 2A ); Paratypes, JUE 15902- 1 ( Fig. 2B ), JUE 15902-2 ( Fig. 2C ), JUE 15902-3 ( Fig. 2D ), JUE 15902-4 ( Fig. 2E ).

Type locality: Kita-Kuroiwa Quarry , Kakizaki-ku , Joetsu City in central Honshu, Japan (see Amano et al. 2010); seep site .

Type horizon: Fossil hydrocarbon seep deposits of the Ogaya Formation, uppermost Middle Miocene.

Dimensions.—See Table 2.

Diagnosis.—Medium-sized Provanna with variable sculpture ranging from sigmoidal axial growth lines and many indistinct spiral cords to strong sigmoidal axial ribs crossed by weaker spiral cords. Whorls with broad, smooth sutural ramp and distinct rounded shoulder, tabulated at axial ribs, where present.

Description. —Medium-sized shell, up to 9.8 mm high, ovate fusiform; teleoconch at least three whorls; protoconch not preserved. Sutures weakly impressed. Body whorl with broad, smooth sutural ramp sloping gently to rounded shoulder. From shoulder abapically body whorl sides gently curved. Ornament variable; some specimens, like holotype ( Fig. 2A ) and paratype JUE 15902-2 ( Fig. 2C ), having whorls with sigmoidal growth lines and many indistinct spiral cords best developed on the body whorl near the shoulder and at whorl base; other specimens, like paratype JUE 15902-3 ( Fig. 2D ) having nearly smooth whorls with sigmoidal growth lines only. Strong sigmoidal axial ribs on apical whorls of some specimens, such as paratype, JUE 15902-4, up to eighteen in number on penultimate whorl ( Fig. 2E ). In some specimens, distinct axial ribs also on body whorl, as in paratype, JUE 15902-1 ( Fig. 2B ). In specimens with axial ribs, spiral cord at shoulder at deflection point in shape of ribs relatively stronger than other spiral cords, forming weak nodes at intersection points with axial ribs.Aperture broad and rounded, with evidence for weak siphonal notch. Shells mostly recrystallized, but relict crossed lamellar structure visible on inner shell surface of one specimen.

Remarks.— Provanna lomana Dall, 1918 from seep, vent, and whale-fall sites off California resembles P. hirokoae in outline, shell size and shape of axial ribs on the apical whorls. However, P. lomana has stronger spiral cords and axial ribs on the body whorl. P. chevalieri Warén and Bouchet, 2009 from seep sites off West Africa is also similar to P. hirokoae in outline and size, but differs in having deeper sutures, a narrower and less sloping sutural ramp, and strong spiral cords on the basal part of the body whorl.

Provanna hirokoae specimens have very variable sculpture, particularly on the early whorls, and share this characteristic with several fossil ( P. antiqua Squires, 1995 and P. marshalli Saether, Little, and Campbell, 2010 ) and modern ( P. variabilis ) species in the genus.

Stratigraphic and geographic range. —From the type locality only.

Figures

Fig. 2. Abyssochrysoid gastropod Provanna hirokoae sp. nov., uppermost Middle Miocene Ogaya Formation (locality 3), Japan. A. Holotype, JUE 15901; apertural (A 1), adapertural (A 2), and apical (A 3) views. B. Paratype, JUE 15902-1; adapertural (B 1), oblique adapertural (B 2), and apical (B 3) views. C. Paratype, JUE 15902-2, apertural view. D. Paratype, JUE 15902-3; adapertural (D 1) and apical (D 2) views. E. Paratype, JUE 15902-4; apertural (E 1), adapertural (E ), and apical (E ) views.