Orbitestella dioi, Hybertsen & Kiel, 2018

Hybertsen, Frida & Kiel, Steffen, 2018, A middle Eocene seep deposit with silicified fauna from the Humptulips Formation in western Washington State, USA, Acta Palaeontologica Polonica 63 (4), pp. 751-768 : 762-763

Orbitestella dioi sp. nov.

Fig. 15 .

Etymology: Named after a musician Ronnie James Dio (1942–2010).

Type material: Holotype: NRM Mo 185034 with two mostly intact whorls with defined sculpture . Paratype: NRM Mo 185033 with elevated spire and intact protoconch .

Type locality: The Satsop Weatherwax seep deposit, Washington State, USA .

Type horizon: Basal Humptulips Formation, middle Eocene.

Material.— Type material only.

Dimensions.— Holotype: 0.75 mm in height and 1.5 mm in width.

Diagnosis.—Discoidal shell with wide umbilicus, a slightly elevated spire, a rounded-pentagonal whorl profile with an apical angle of 105°, with dimensions at least 0.75 mm in height and a diameter of 1.5 mm.

Description.—Protoconch diameter approximately 0.2 mm, terminates in thin varix, probably smooth. Teleoconch has three whorls with ~25 prominent, evenly spaced axial ribs, at least 12 weaker spiral ribs in reticulate pattern on spire; sinuous growth lines, ophistocline on shoulder, prosocyrt on periphery. Umbilicus deep, width around 1/3 of shell diameter, sculptured with strong axial ribs and finer spiral ribs; rounded aperture with sinuous peristome.

Remarks.—Shares the general shell sculpture and size dimensions with the Recent Orbitestella patagonica Simone and Zeyala, 2004 but has fewer axial ribs and less prominent spiral ribs. In O. patagonica the spiral ribs are more prominent than the axial ribs, which is the opposite from O. dioi sp. nov. A similar reticulate pattern on the outer surface of the shell is also found on the Recent Orbitestella bermudezi Aguayo and Borro, 1946 along with a sinuous peristome and rounded aperture, however in O. bermudezi the intersections between the axial ribs and spiral cords form pointed nodules and the aperture is subtriangular, which differs from O. dioi sp. nov. The prominent vertical ribs on the whorls of Orbitestella granulata Lozouet, 1998 , from the Oligocene of France ( Lozouet 1998) are coarser than on O. dioi and the former is also missing a reticulate ornamentation. Orbitestella palaiopacifica Squires and Goedert, 1996b from the Eocene of the Crescent Formation, North America lacks the spiral ribs on the whorls as well as an elevated spire. The organization of the growth lines on O. dioi follows the same pattern as the Recent Lurifax goederti (Kiel, 2006) but lacks the strong angulation and prominent spiral cords. Lurifax was placed within the family Orbitestellidae ( Warén and Bouchet, 2001) . Recently Lauridsen et al. (2014) reported an orbitestellid from the Faxe Formation, Denmark that is larger than our specimens and with a distinctively larger protoconch. O. dioi shares many features with the orbitestellids compared above, however, it does not fit to any already described species and therefore we describe this new species.

Stratigraphic and geographic range.— Type locality and horizon only.

Figures

Fig. 15. The orbitestellid gastropod Orbitestella dioi sp. nov. from the middle Eocene Satsop Weatherwax seep deposit, Washington State, USA. A. NRM Mo 185033; specimen with 2.25 whorls in apical view (A1); apertural view showing a rounded aperture (A2); close-up on protoconch, arrow indicates protoconch-teleoconch transition (A3). B. NRM Mo 185034 (holotype) with roughly 2 whorls in apical (B1) and oblique (B2) views; close-up on protoconch (B3).