Hokkaidoconcha, Kaim, Jenkins & Waren, 2008

Nakrem, Hans Arne, 2017, Gastropods from the Late Jurassic - Early Cretaceous seep deposits in Spitsbergen, Svalbard, Zootaxa 4329 (4), pp. 351-374 : 358

Hokkaidoconcha sp.

( Fig. 5I –M )

2015 Hokkaidoconchidae gen. et sp. indet.; Hryniewicz et al. 2015a, table 1.

Description. Cerithioid shell with opisthocline to slightly opisthocyrt axial ribs and fine numerous spiral riblets. Whorl flanks are weakly inflated and the suture weakly incised. Protoconch and aperture not preserved.

Material and occurrence: Three specimens from seep #12, Sassenfjorden, Svalbard; late Berriasian (Early Cretaceous). All illustrated: PMO 217.507, PMO 217.509, PMO 217.511b.

Remarks. Hokkaidoconcha sp. is represented by three incompletely preserved juvenile specimens, so several pertinent shell characters could not be observed, and this is the reason why we decided to leave this species in open nomenclature. Our Hokkaidoconcha sp. from Svalbard is most similar to juveniles of the Cenomanian H. tanabei from Japan ( Kaim et al. 2008b). The latter species, however, grows to a relatively large size and its ornament changes with ontogeny. Changes in ontogeny could not be observed in Hokkaidoconcha sp. from Svalbard due to the fragmentary preservation. Another similar species is H. occidentalis ( Stanton, 1895) from the Late Jurassic– Early Cretaceous of California ( Kiel et al. 2008; Kaim et al. 2014) which seems, however, to have a much weaker developed spiral ornamentation and stronger axial ribs. Hokkaidoconcha hignalli Kaim & Kelly, 2009 from the Tithonian (Late Jurassic) Gateway Pass seep on Alexander Island, Antarctica, loses the ornamentation during ontogeny and may thus actually belong to the genus Hudlestoniella (see below). Superficially, Hokkaidoconcha sp. is similar to juvenile specimens of Hudlestoniella hammeri (see below), but it differs in having stronger and persistent spiral ornament (which at the size of Hokkaidonconcha sp. already fades away in H. hammeri ) and opistocline to weakly opistocyrt axial ribs, rather than strongly opistocyrt ribs as observed in H. hammeri .

Figures

FIGURE 5. A – H. Hudlestoniella hammeri sp. nov. Seep deposit # 9, Sassenfjorden, Svalbard; late Berriasian (Early Cretaceous). A, B, F. Holotype (PMO 224.754). C, G, H. Paratype (PMO 224.755). D. PMO 224.756. E. PMO 224.757. I – M. Hokkaidoconcha sp. Seep deposit # 12, Sassenfjorden, Svalbard; late Berriasian (Early Cretaceous). I. PMO 217.509. J, L. PMO 217.511 b. K, M. PMO 217.507.