Desbruyeresia belliatus, 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 : 758-760

Desbruyeresia belliatus sp. nov.

Fig. 13 . Etymology: From Latin belliatus , plump; referring to the appearance of the shell.

Type material: Holotype: NRM Mo 185025 consisting of an almost fully intact shell with distinct sculpture . Paratypes: NRM Mo 185022–24 ; NRM Mo 185026, four specimens with distinct shell features .

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

Type horizon: Basal Humptulips Formation, middle Eocene.

Material.— Type material and approximately 230 unnumbered specimens at NRM from the type locality. Three specimens are deposited in the Burke Museum ( UWBM 108851–53 ) .

Dimensions. — Holotype: 3.78 mm high and 1.54 mm wide.

Diagnosis.— Thick and sturdy high-spired shell with rounded whorls, strong axial sculpture forming nodes at axial-spiral intersections, apical angle approximately 45° reaching at least 5 mm in height and 3 mm in width.

Description.—Protoconch: up to 4 whorls; protoconch is decollated, silicified calcareous plug filling topmost whorl; maximum diameter 0.5 mm, minimum height 0.5 mm, sculptured by reticulate pattern, ~30 prominent, slightly ophistocline axial ribs, 14 weaker spiral ribs across whorl; aperture not thickened, teleoconch transition visible on fourth whorl. Teleoconch: up to four whorls; sculptured by reticulate pattern, ~12 slightly opisthocline axial ribs, at least four spiral ribs, prominent nodes in oblique angle toward apex at intersections; adapical row of nodes on each whorl strong, successively weaker towards base of whorl; whorls slightly convex, incised sutures; basal margin marked by thick spiral cord; base has up to 5 spiral cords, downwards decreasing in strength; aperture oval with short, rounded siphonal notch; columella smooth; thin parietal callus.

Remarks. —Distinguishable from Provanna based on its more slender shell ( Warén and Bouchet 1993) and the shell has “axial ribs, spiral cords, knobs and occasionally short spines” ( Desbruyères et al. 2006), features that most of which are present in the species from Satsop Weatherwax, making it a likely member of Desbruyeresia . Type species Desbruyeresia spinosa Warén and Bouchet, 1993 is characterized by prominent spines forming at the crossings of the axial and spiral ribs on the whorls of the teleoconch, which can also be seen in Desbruyeresia cancellata Warén and Bouchet, 1993 . No spines can be seen on D. belliatus , instead the shell structure more resembles that of Desbruyeresia melanioides Warén and Bouchet, 1993 with small nodes forming at the intersections of the ribs. D. melanioides have slightly curved axial ribs, but not as strongly ophistocline as seen on D. belliatus . The whorls of Desbruyeresia marianaensis have six or more spinal cords and there are no prominent nodes at the intersections of the apical and spinal cords as on D. belliatus . Desbruyeresia antiqua Bandel and Kiel, 2000 from a Late Cretaceous slump deposit in Spain is quite different from Desbruyeresia belliatus by having sharp axial ribs with a single, central row of spines. The species is based on a single specimen and its placement in Desbruyeresia has been questioned ( Kaim et al. 2008), but without further material, these doubts can neither be confirmed nor rejected. The reticulate pattern on Desbruyeresia chamorrensis Chen, Ogura, and Okutani, 2016 is made up by three spiral cords whereas in D. belliatus there are at least four and D. belliatus is generally smaller. The reticulate pattern on the protoconch and the pointed nodes on the spire of D. belliatus closely resembles that of Desbruyeresia kanajirisawensis Kaim, Jenkins, and Warén, 2008 from the Cretaceous of Japan ( Kaim et al. 2008) and the calcareous plug described in D. kanajirisawensis is also present in D. belliatus , however D. kanajirisawensis displays six nodes making up a tight reticulate pattern whereas D. belliatus is of larger size and only has five nodes making up a wider pattern.

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

Figures

Fig. 13. The provannid gastropod Desbruyeresia belliatus sp. nov. from the middle Eocene Satsop Weatherwax seep deposit, Washington State, USA. A. NRM Mo 185022; almost complete specimen showing protoconch with 3 whorls (A1); close-up on protoconch (A2); spire with 2.5 whorls and the spire base with short siphonal notch, arrows pointing to spiral cords (A3). B. NRM Mo 185023; protoconch with 3.5 whorls showing the protoconch-teleoconch transition (B1); close-up of protoconch sculpture (B2); close-up of protoconch-teleoconch transition (arrow) (B3). C. NRM Mo 185024; decollated protoconch and calcareous plug (C1); close-up on protoconch (C2). D. NRM Mo 185025 (holotype) showing protoconch with 3 whorls and teleoconch with 3.5 whorls and an oval aperture. E. NRM Mo 185026, Close-up of specimen with protoconch-teleoconch transition (arrow).