Desbruyeresia, WAREN & BOUCHET, 1993

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 : 425-427

GENUS DESBRUYERESIA WARÉN & BOUCHET, 1993

Type species: Desbruyeresia spinosa Warén & Bouchet, 1993 . Recent ; North Fiji Basin .

DESBRUYERESIA KANAJIRISAWENSIS SP. NOV.

( FIGS 2A–C, G, H, P, S, 3A)

Derivation of name: After the type locality.

Type material: UMUT MM29355 (holotype), adult or adolescent shell ; UMUT MM29356 (paratype), juvenile shell with decollate protoconch preserved ; UMUT MM29357 (paratype), another juvenile shell with protoconch .

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

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

Description: Shell ( Fig. 2A) of medium size and melanoid in shape with strong axial and spiral sculpture. The protoconch is decollated; the top of the second larval whorl is filled with a calcareous plug ( Fig. 2S). Protoconch clearly demarcated from teleoconch; whorls ornamented by c. 24–26 orthocline axial ribs and 9–10 weaker spiral ribs ( Fig. 2B, C, G, H, P, S). Initial teleoconch whorl with five spiral ribs which form weak and progressively stronger nodes and a reticulate pattern with the sturdy axial ribs (c. 13 per whorl). Number of spiral cords constant during ontogeny. Whorls angulated at most apical rib. Nodes at most apical ribs more pointed and directed obliquely toward apex. Suture moderately incised and whorls moderately convex. Growth lines distinct. Base rounded, not clearly demarcated from lateral flank. ·

Axial ribs weaker on base; only spiral ribs and growth lines distinct there. Aperture not fully preserved but apparently rounded with no trace of siphonal channel or notch.

Dimensions: Holotype ( UMUT MM29355 ) composed of five whorls: maximum shell height 7.8 mm, diameter 3.0 mm . Paratype ( UMUT MM29356 ): maximum height of decollated protoconch 0.62 mm, diameter 0.55 mm .

Remarks: This species is the most common gastropod in the Kanajirisawa locality. The teleoconch of D. kanajirisawensis is reminiscent of the Recent Desbruyeresia melanioides Warén & Bouchet, 1993 , which, by contrast, has only three spiral ribs. The protoconch is of typical provannid multispiral type both in the pattern of ornamentation and decollation (compare Warén & Bouchet, 1993: fig. 44C–E and Fig. 4A, B, E herein).

UNNAMED PROVANNID SPECIES

Yasukawa provannid ( Fig. 3D, E, I): The provannids at Yasukawa are poorly preserved and no protoconch has been found for these specimens. The best preserved specimen ( UMUT MM 29363) is a juvenile teleoconch composed of three whorls, but lacking an aperture, as usual. The terminal whorl, the best preserved one, is ornamented by two median spiral ribs and an additional weaker one in the apical portion of the whorl. It has a generalized Provanna -like appearance and resembles the Omagari provannid. The difference in ornamentation might be caused by different ontogenetic stage and/or preservation. The specimens are considered to be too poorly preserved to be named.

Gakkonosawa provannid ( Fig. 3G, H): The provannid from Gakkonosawa is represented by two specimens. The better preserved specimen ( UMUT MM 29364) consists of one teleoconch whorl with no protoconch preserved. The teleoconch is ornamented by three sturdy spiral ribs. The two on the medial part of the whorl are stronger and the one on the apical part is weaker. At the intersections with the sturdy orthocline axial ribs there are blunt but distinct nodes. Moreover, the shell surface is ornamented by an irregular micropattern ( Fig. 3H), as is frequently the case in modern species of Provanna . The provannid from Gakkonosawa is similar to provannids from Omagari and Yasukawa and differs mainly by more sturdy ornamentation, which may be intraspecific variability.

Omagari provannid ( Fig. 3F, J): The best preserved provannid from Omagari ( UMUT MM 29362) consists of about one teleoconch whorl lacking the protoconch. The shell is ornamented by orthocline sturdy axial ribs and two small weaker spiral ribs with blunt nodes at the intersections. The preserved part of the shell strongly resembles the early whorls of the Recent Provanna buccinoides Warén & Bouchet, 1993 from off Fiji (compare Warén & Bouchet, 1993: fig. 54B) but fragmentary preservation excludes any further identification.

Figures

Figure 4. Juvenile Recent Provannidae and Abyssochrysidae (A–D) and patterns of shell decolation and preservation (E–F). A, E, Desbruyeresia spinosa Warén & Bouchet, 1993 from North Fiji Basin (specimen illustrated also in Warén & Bouchet, 1993: fig. 44D). A, decollate protoconch; E, details of decollation; note no signs of shell abrasion on the protoconch edges B, decollated protoconch of Alviniconcha hessleri Okutani & Ohta, 1988 from north Fiji Basin (specimen illustrated also in Warén & Bouchet, 1993: fig. 44C). C, paucispiral protoconch of Provanna segonzaci Warén & Ponder, 1991 from Lau Basin. D, Abyssochrysos sp. from off New Caledonia; note axial ribs and spiral riblets at the beginning of paucispiral protoconch. F, decollation pattern of terrestrial gastropod Rumina decollata Linné, 1758. G, typical pattern of in-vivo apex erosion in Phymorhynchus sp. shell from the Lucky Strike site on the Mid-Atlantic Ridge; note shell surface abrasion but no sign of decollation.