Paskentana umbilicata, Kiel & Campbell & Gaillard, 2010

Kiel, Steffen, Campbell, Kathleen A. & Gaillard, Christian, 2010, New and little known mollusks from ancient chemosynthetic environments, Zootaxa 2390 (1), pp. 26-48 : 34

Paskentana umbilicata sp. nov.

( Fig 5 °, B)

Diagnosis: Biconical shell; whorls with crenulate, subsutural collar; entire shell covered by fine spiral threads that are about as wide as the spaces separating them; wide umbilical slit.

Holotype: Holotype 10.5 mm high and 7 mm wide, from Beauvoisin ( FSL 286 456) .

Additional material: Several additional specimens that are preserved as either external or internal molds.

Type locality and strata: Seep deposits at Beauvoisin, Drôme, France, 44°18’N, 5°12’E; Late Jurassic, Oxfordian .

Description: Biconical shell, four or more whorls, suture groove-like, resulting from thin, crenulated collar formed by succeeding whorl, which extents slightly above line of attachment; whorls slightly constricted below the suture, especially on later whorls, slightly and evenly convex below; sculpture of numerous fine, sharp-crested spiral cords, of increasing number during ontogeny, 14 cords on penultimate whorl, 7 on preceding one; spiral cords of crenulate appearance resulting from numerous fine, strongly prosocyrt growth increments, interspaces between spiral cords about two times as wide as spirals themselves; basal margin well-rounded, base with 22 subequally sized additional spiral cords having the same appearance as those on shell flank, third-last cord before umbilical slit much stronger; umbilical slit wide, bordered by strong cord or keel, interior of umbilical slit smooth; aperture lenticular, columellar lip reflected near parietal area but parietal area not callused; columella straight, smooth, basal part missing but possibly with siphonal notch. Largest specimen 21 mm high, 12 mm wide.

Remarks: The most similar of the three Californian Paskentana species is P. globosa Kiel, Campbell, Elder & Little, 2008 , which differs mainly in being more globular, larger, and lacking the fine, crenulated collar around the suture. For differences to Paskentana anistratenkorum n. sp. see below.

We have two specimens of Paskentana umbilicata sp. nov. that seem to have a much broader last whorl and possibly also a much wider umbilicus than the others, but they are too poorly preserved to decide whether they warrant separation as a separate species. At the late Jurassic to early Cretaceous seeps in California occurs a pair of species ( Paskentana paskentaensis and P. berryessaensis ) having very similar sculpture but differing mainly in the width of the last whorl (Kiel et al. 2008).

Distribution: Type locality only.

Etymology: For its well-developed umbilical slit.

Figures

FIGURE 5. A, B. Paskentana umbilicata n. sp. from Oxfordian (Late Jurassic) seep carbonates at Beauvoisin, southeastern France; A, holotype (FSL 286 456), B, specimen with broad last whorl (FSL 286 457). C. Paskentana anistratenkorum n. sp. from a Hauterivian (Early Cretaceous) seep carbonate in the Planerskoje section, Crimea, Ukraine; holotype (USNM 535873).