Provanna, DALL, 1918

Kaim, Andrzej, Jenkins, Robert G. & Warén, Anders, 2008, Provannid and provannid-like gastropods from the Late Cretaceous cold seeps of Hokkaido (Japan) and the fossil record of the Provannidae (Gastropoda: Abyssochrysoidea), Zoological Journal of the Linnean Society 154 (3), pp. 421-436 : 423-425

GENUS PROVANNA DALL, 1918

Type species: Trichotropis (Provanna) lomana Dall, 1918 . Recent; US Pacific Coast.

PROVANNA TAPPUENSIS SP. NOV.

( FIGS 2K–M, O, Q, 3C)

Derivation of name: After the town of Tappu, located close to the type locality.

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Type material: UMUT MM29359 (holotype), adolescent shell with no protoconch ; UMUT MM29358 (paratype), juvenile shell with protoconch .

Type locality: Kanajirisawa Creek , Tappu area, Hokkaido, Japan .

Type horizon: Middle Cenomanian (Late Cretaceous) carbonate seep deposits.

Description: Shell ( Fig. 2M) sturdily built, of medium size and rissoid-like shape, with strong axial and spiral sculpture. Protoconch ( Fig. 2K–L) decollate; top remaining 1+ larval whorl filled with a calcareous plug ( Fig. 2L); maximum diameter 0.65 mm; sculptured with about 20–30 (estimate) orthocline axial ribs of uniform strength from suture to suture; and about nine much less prominent spiral cords. Initial teleoconch whorl with one strong median and two, supra- and infra-sutural spiral ribs which form strong nodes and a reticulate pattern with the axial ribs (c. 15 per whorl). With increasing size the number of spiral ribs increases to about five (plus about five on the basal surface), the reticulation becomes less pronounced and the whorls evenly rounded instead of medially keeled. Columella straight. Peristome and siphonal canal (if any) not preserved.

Dimensions: Holotype ( UMUT MM29359 ): maximum shell height 3.88 mm, diameter 2.57 mm . Paratype ( UMUT MM29358 ): maximum height of incomplete protoconch 0.35 mm, diameter 0.65 mm .

Remarks: The teleoconch is quite similar to several Recent species of Provanna , but all modern species of Provanna have a paucispiral protoconch. It may, however, be assumed that the early members of Provanna had a planktotrophic development, or that Desbruyeresia , with such development, is a branch of Provanna that has retained planktotrophy. The larval shell of P. tappuensis resembles that of Desbruyeresia kanajirisawensis sp. nov. (see below) but has slightly stronger axial ribs and the whorls more convex. The teleoconch of P. tappuensis is much less elongate and has an angulation on the juvenile whorls whereas the shell of D. kanajirisawensis is strongly elongate and the juvenile whorls are not angulated.