Taxonomic re-evaluation of Ericiolus and Mercedesia (Prymnesiophyceae) and description of three new species

ABSTRACT The genera Ericiolus and Mercedesia are distinctive extant coccolithophores that are characterized by monothecate, monomorphic coccospheres with one type of triradiate star-shaped nannoliths. The two genera were described from the Danish coastal waters, the surface waters of the Arctic, and the Southern Oceans. During a study of samples from the low photic zone of the Mediterranean and Sargasso Seas, and from the subtropical gyres of the South-eastern Pacific and the South Atlantic Oceans, 44 collapsed coccospheres with triradiate star-like nannoliths were observed via scanning electron microscopy. Observations on the morphologies and biometric assessments of these specimens revealed that three distinct sets of nannoliths can be distinguished and that these were morphologically differentiated from all currently known species of Ericiolus and Mercedesia. The new forms and the previously described species of Ericiolus and Mercedesia were, however, similar, as they all demonstrated a distinctive set of collectively shared morphological characters and almost identical size ranges. On the basis of this, and instead of describing a third genus for the same group of nannoliths, we preferred to taxonomically synonymize Mercedesia with Ericiolus and revise the definition of Ericiolus. Therefore, we describe three new species, Ericiolus bendifii sp. nov., Ericiolus sheldoniae sp. nov. and Ericiolus mattioliae sp. nov., and an incompletely defined taxon, as Ericiolus cf. bendifii, and establish the new combinations E. aspiphorus comb. nov., E. multistellatus comb. nov. and E. pusillus comb. nov.