Phanerolepida onoensis, Kaim, Andrzej, Jenkins, Robert G., Tanabe, Kazushige & Kiel, Steffen, 2014

Kaim, Andrzej, Jenkins, Robert G., Tanabe, Kazushige & Kiel, Steffen, 2014, Mollusks from late Mesozoic seep deposits, chiefly in California, Zootaxa 3861 (5), pp. 401-440 : 409

Phanerolepida onoensis sp. nov.

( Fig. 3 J–O)

Diagnosis. Shell turbiniform with weakly convex whorls. Surface ornamented by net-like rhombohedral pattern (referred to as shagreen). Wide, weakly incised ramp present in adapical portion of the flank. Ramp ornamented by four spiral ribs.

Holotype: CAS 73130, H = 9.1 mm, W = 8.0 mm.

Paratype: CAS 73131, H = 11.4 mm, W = 10.0 mm.

Type locality and strata: Eagle Creek, 10 m above the junction with North Fork of Cottonwood Creek, Shasta County, California, USA (for details see Jenkins et al. 2013). Great Valley Group, Budden Canyon Formation, Lower Chickabally Mudstone Member; Late Barremian (Early Cretaceous).

Description. Protoconch unknown. Shell turbiniform with four whorls preserved. Apex abraded, thin external prismatic layer mostly peeled off exposing thick inner nacreous layer. Whorls weakly convex covered by rhombohedric pattern referred to as shagreen by Watson (1879) and Dall (1907). Adapical ramp wide and shallow and ornamented by four spiral ribs. Aperture and umbilical area not preserved.

Remarks. Phanerolepida is a turbinid genus based on the Recent deep-water species Turbo transenna Watson,1879 from Japan. Okutani & Iwahori (1992) report a bathymetric range of 550–1100 m for that species, which overlaps with the bathymetric range of hydrocarbon seep sites occurring in the same area. There are also a few fossil species described from Oligocene and Miocene/Pliocene deep-water sediments on the Pacific coast of North America (see Hickman 1972 for a review). Nonetheless, Phanerolepida has not been reported from seep communities so far. Therefore it might be an fortuitous occurrence of this species at the Eagle Creek seep deposit. Phanerolepida onoensis differs from Recent and Cenozoic Phanerolepida species in having a much higher shell profile ( Hickman 1972).

Distribution. Type locality only.

Etymology. After the community of Ono, near which the type locality is located.

Figures

FIGURE 3. A. Limpet gastropod indet. from Valanginian (Early Cretaceous) seep carbonates at Bear Creek, Colusa County, California, USA; GZG. INV. 84967. B – D. Chilodonta? reticulata sp. nov. from Valanginian (Early Cretaceous) seep carbonates at Bear Creek, Colusa County, California, USA; holotype (GZG. INV. 84971). E – I. Hikidea osoensis sp. nov. from Valanginian (Early Cretaceous) seep carbonates at Bear Creek, Colusa County, California, USA. E – G. Holotype (GZG. INV. 84968). H. Paratype (GZG. INV. 84969). I. Juvenile (GZG. INV. 84970) displaying ornamentation of the early ontogenetic stage of the shell. J – O. Phanerolepida onoensis sp. nov. from Late Barremian (Early Cretaceous) seep site at Eagle Creek, Shasta County, California, USA; holotype (CAS 73130). J – K. Lateral views. L. Apical view. M. External prismatic shell layer. N. Internal nacreous shell layer. O. Detail of rhombohedric ornament pattern.