Bathypurpurinopsis, Kiel & Campbell & Elder & Little, 2008

Kiel, Steffen, Campbell, Kathleen A., Elder, William P. & Little, Crispin T. S., 2008, Jurassic and Cretaceous gastropods from hydrocarbon seeps in forearc basin and accretionary prism settings, California, Acta Palaeontologica Polonica 53 (4), pp. 679-703 : 693

Genus Bathypurpurinopsis nov.

Etymology: A Purpurina −like gastropod from bathyal depth.

Type species: Bathypurpurinopsis stantoni sp.nov. Great Valley Group , Early Cretaceous , Cold Fork of Cottonwood Creek, Tehama County, California, USA .

Diagnosis.—Moderately high−spired fusiform to littoriniform shell with several evenly convex whorls and incised suture, sculpture may consist of fine spiral threads crossed by slightly sinuous growth lines. Aperture broadly lenticular, with siphonal notch and short and pointed siphonal column, columella with prominent siphonal fold.

Discussion.—Protoconch and shell microstructure are unknown. This new genus has an interesting combination of characters for Early Cretaceous gastropods. The spire resembles that of modern Littorinidae or Mesozoic Ampullinidae Cossmann, 1918 ( Ampullospiridae Cox, 1930 of some authors), for example Pictavia Cossmann, 1925 . These taxa, however, differ markedly from Bathypurpurinopsis gen. nov. in their apertural features. The siphonal notch and the prominent siphonal fold of the aperture are very similar to those seen in modern neogastropods, especially among muricids, buccinids, and cancellariids.

Some members of the Mesozoic Purpurinidae have columellar and siphonal features like Bathypurpurinopsis including a fold and corresponding notch (e.g., the Cretaceous Purpuroidea Lycett, 1848 ). Most purpurinids, however, have a strongly angular shoulder, and axial and tuberculate sculpture. An exception to this is the Middle Jurassic genus Ochetochilus Cossmann, 1899 , which, like Bathypurpurinopsis , has only fine spiral sculpture, mainly convex whorls, a rather long siphonal canal, but lacks a siphonal fold. However, that genus is only poorly known and even its position within the Purpurinidae is uncertain.

The siphonal fold suggests neogastropod or cassoidean affinities, but Early Cretaceous members of these groups have quite different shell shapes ( Taylor et al. 1983). Thus Bathypurpurinopsis gen. nov. might either represent a very early radiation of neogastropods into the seep environment, or a rather late member of the mainly Triassic and Jurassic Purpurinidae .

Stratigraphic and geographic range.—Early Cretaceous cold−seep carbonates in the Great Valley Group of California, USA.