Diatoms in upper Pliocene–lower Pleistocene sediments, subpolar North Atlantic: 5. Thalassiosira lindstroemii

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Despite its phylogenetic importance, Thalassiosira lindstroemii has received little attention to date. In this study, the morphology of T. lindstroemii was examined in detail from upper Pliocene sediments of the subpolar North Atlantic. The valve has a valve face with linear areolation and scattered fultoportulae, a valve face/mantle junction with a single rimoportula and spines developed from triangular bases, and a mantle area with marginal fultoportulae and ribs. Both the valvocopula and second copula possess a characteristic ring of poroid areolae arranged along the advalvar margin. There is no doubt that T. lindstroemii is closely related to T. eccentrica, a major Thalassiosira species, because they possess many common morphological characteristics. Distinct differences between the two species include only the valve face areolation and the position of poroid areolae in the valvocopula. Although additional research is needed to reveal the precise phylogenetic relationship, the close morphological similarities suggest that T. lindstroemii is an ancestral (or possibly descendant) species of T. eccentrica.