Hikidea, 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 : 407-408

Genus Hikidea gen. nov.

Type species. Hikidea osoensis sp. nov.; see below.

Diagnosis. Small turbinid shell, flat-topped with concave subsutural ramp or finely pleated subsutural cord, otherwise smooth or, in some species, with highly variable spiral ornamentation. Ultimate whorl usually with slightly dropping suture line, generating curve circular, aperture tangential, peristome uninterrupted. Outer lip smooth, inner lip with some callus. Umbilicus absent.

Species included. The type species, Cantrainea yasukawensis Kaim et al., 2009 , and Cantrainea omagariensis Kaim et al. 2009 , all three from fossil hydrocarbon seep deposits, the "globular skeneiform gastropod" from a Late Cretaceous wood fall association ( Kiel et al. 2009), and "vetigastropod gen. et sp. indet." from a Late Cretaceous plesiosaur-fall association ( Kaim et al. 2008a). The extant species Cantrainea nuda Okutani, 2001 from Minami Ensei Knoll, Okinawa Through, Japan may also belong here but it needs further research and collection effort.

Remarks. The species assigned here to Hikidea occur in several ancient chemosynthesis-based associations, mostly hydrocarbon seep deposits (Kaim et al. 2009 and herein), and also at a Cretaceous reptile fall ( Kaim et al. 2008a) and a Cretaceous wood fall ( Kiel et al. 2009). The Recent species Cantrainea nuda Okutani, 2001 collected from the Minami Ensei Knoll has not been reported to occur in a chemosynthesis −based community by Okutani (2001) in the original description, but a hydrothermal vent community has been described from this locality by Hashimoto et al. (1995). Therefore, it is possible that C. nuda is a member of this type of community. Cantrainea nuda is known from a single shell with dried animal inside, which was not examined by Okutani (2001). Its shell is very similar to Hikidea but differs slightly in having a finely pleated subsutural cord rather than a subsutural ramp and by having a small knob on the inner lip (this feature is absent in the known Cretaceous species). The species of Cantrainea s.s. have much larger shells and strong spiral ornamentation (compare e.g. Okutani & Fujikura 1990 and Warén & Bouchet 1993). Thanks to the courtesy of Anders Warén (Stockholm) and Paul Callomon (Philadelphia), we received photos of the figured syntype (ANSP IP4243) of the type species of Ataphrus Gabb, 1869 , A. crassus Gabb, 1869 . The specimen is very similar to Hikidea omagariensis in gross shell morphology though its surface and apertural region are badly eroded so no details could be examined. The type locality of this specimen is unclear. Gabb (1869, p. 171) wrote: "Rare in the Martinez Group (?) at Martinez. Specimens were sent me by Mr. Mathewson, but not so labelled that I can determine their horizon, and they are so carefully trimmed outof the matrix that I have no associated species to assist me." Gabb (1869) considered the Martinez Group to be Cretaceous though subsequent work showed it to be Eocene ( Wilmarth 1931; Watson 1942). Small patches of Great Valley Group also crop out in this area so that without additional collection effort, it seems to be impossible to determine the age of that taxon. The situation is additionally complicated by the usage of the generic name Ataphrus for a wide array of species from Jurassic and Cretaceous sediments worldwide ( Monari et al. 1996; Kaim 2004; Gründel & Kaim 2006; Gründel 2008), which may actually belong to entirely different taxa. In summary, we are aware that Hikidea n. gen. could potentially be a synonym of Ataphrus , but due to the poor preservation of the type of Ataphrus , as well as uncertainties regarding its type locality and age, which will make it difficult to obtain topotype material, we consider Ataphrus a nomen dubium.

Stratigraphic range. Valanginian (Early Cretaceous) to Campanian (Late Cretaceous).

Etymology. For Yoshinori Hikida who collected several specimens of this genus in the Nakagawa region.