Abstract
Rhaphoneis amphiceros (Ehrenberg) Ehrenberg is one of the commonest extant rhaphoneid diatoms and has been reported from multiple fossil deposits, but our work suggests this taxon may not be as common in the fossil assemblages as indicated by the literature. Indeed, the original description of the species, made by Ehrenberg, is not as detailed as modern descriptions, which can lead to confusion when identifying taxa. Recent studies show that diatom species previously reported to occur over time intervals of tens of millions of years may actually represent groups of taxa lumped together due to inaccurate identifications. In this article, we present two new species that, without careful SEM examination, can be confused with R. amphiceros. These new species, interpreted to represent two new genera in the Rhaphoneidaceae, were found in middle Eocene sediments from Ocean Drilling Program (ODP) Hole 1050A (30°06’N, 76°14.1’W), drilled on Blake Nose, western North Atlantic. Rhomboneis shtapovii Figus & Witkowski and Rosaforma paillesiae Figus & Witkowski show unique morphological characteristics that lead us to create new genera. Rhomboneis shtapovii has two rimoportulae per valve and an unusual type of velum occluding the areolae. Rosaforma paillesiae has a peculiar asymmetric apical pore field occupying half the valve pole, the other half contains a rimoportula with two apical pores.
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