Abstract

The late Albian planktonic foraminifera Hedbergella trocoidea yezoanaTakayanagi and Iwamoto, 1962, from Japan, whose primary distinguishing feature is 7–8 chambers in the final whorl, has been internationally cited with a species rank as Hedbergella yezoana. Still, its taxonomic position is not well understood, as manifested by the fact that published hypotypes have six or fewer chambered forms, and such ambiguity is due partly to a lack of updated knowledge about the primary types (a holotype and single paratype), topotypes, and hypotypes from the northwestern Pacific region. This study reexamines the species concept of Hd. yezoana through uncoated SEM observations of the primary types and newly obtained type-locality material. The holotype is synonymous with Ticinella primula Luterbacher, 1963, as judged by its uneven wall surface, pseudoplanispiral (slightly streptospiral) mode of coiling, somewhat tangentially elongate last chambers, and a possible porticus-like structure. The topotypes exhibit important characters such as supplementary apertures and well-developed portici, thus confirming the synonymy of Hd. yezoana and T. primula. This outcome, however, is troublesome because T. primula is the widely used name for this morphology, and accepting the priority of “Ticinella yezoana” affects the nomenclatural stability in Cretaceous planktonic foraminifera. Conservation of the junior name T. primula is supported not only by the insufficient preservation of the Hokkaido material but also by the concept of Article 23.9 (reversal of precedence) in the International Code of Zoological Nomenclature (4th edition, 1999), although a ruling from the Zoological Commission would be eventually necessary. The paratype, in contrast, exhibits a smooth, microperforate wall, and is identified in open nomenclature as Microhedbergella sp. A (multi-chambered form). In addition to this wall-surface feature, this potential new Microhedbergella taxon differs from the “Hd. yezoana” holotype (and hence from T. primula) by lacking a streptospiral mode of coiling, exhibiting isomorphic globular chambers between the umbilical and spiral sides, and possessing a very poorly developed or nearly absent lip.

The type-locality assemblage of “Hd. yezoana” is marked by the common occurrence of several other “ticinellid” taxa (Biticinella breggiensis and at least three species of Ticinella) and Microhedbergella with very rare Favusella. The Microhedbergella specimens have a remarkably wide range of morphologies, some comparable to those recorded in a local Texas assemblage, but the rest undescribed.

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