Fossil remains of ciliates (phylum Ciliophora): A recommendation for their treatment under the International Code of Nomenclature for algae, fungi and plants

Ciliates (phylum Ciliophora) are a diverse group of ciliated protists common in marine, freshwater, and terrestrial environments. Ciliates are traditionally treated under the International Code of Zoological Nomenclature (ICZN) as “animals” although many are non-constitutive phototrophs. As alveolates, ciliates are closely related to the dinoflagellates, which are treated today under the International Code of Nomenclature for algae, fungi and plants (ICN). The fossil remains of ciliates, primarily the resting cysts and loricae, are frequently encountered in palynological preparations of modern and older marine and nonmarine deposits. They have strong potential for use in paleoenvironmental reconstructions but most cannot be linked unequivocally to their corresponding non-fossil motile stage. A separate taxonomy is required for fossil ciliate remains and a corresponding formal nomenclature to track their occurrences. The ICZN explicitly prohibits separate names for different stages in the life cycle of a single organism. We therefore recommend placing these fossils under the governance of the ICN, which allows the names of fossil-typified species to coexist with those of their non-fossil-typified equivalent stages (dual nomenclature). We return the ciliate fossil-genus Halodinium Bujak, 1984 to the ICN and recommend the establishment of equivalent fossil-genera for the important non-fossil genera Hexasterias Cleve, 1900 and Radiosperma Meunier, 1910, which are now known to be ciliate cysts. The acritarch genus Cyclopsiella Drugg and Loeblich, 1967 most likely represents ciliate resting cysts and extends to the Jurassic. Placing fossil ciliates under the ICN is a practical solution given that nomenclature serves taxonomy, not the other way around. • Fossil remains of ciliates especially their resting cysts. • The plant–animal divide in phylogenetic classification. • A dual nomenclature approach to fossil ciliates.