Taxonomic reassignment of Pseudohaptolina birgeri comb. nov. (Haptophyta)

The haptophyte genus Pseudohaptolina (formerly Chrysochromulina clade B1-3) currently harbors two species: Pseudohaptolina arctica and Pseudohap-tolina sorokinii. In addition, Chrysochromulina birgeri is expected to belong to this genus due to its morphological similarity to P. sorokinii, but has not yet been genetically characterized. A strain belonging to Pseudohaptolina was brought into culture from Arctic waters, characterized by 18S and 28S rRNA gene sequencing as well as optical and transmission electron microscopy, and deposited in the Roscoff Culture Collection with the code RCC5270. Molecular and morphological data from RCC5270 were compared with those from previously described Pseudohaptolina and Pseudohaptolina-like species. Strain RCC5270 showed strong phylogenetic affinity to P. sorokinii, but TEM observations showed that RCC5270 possesses three types of organic body scale, rather than two as originally described in P. sorokinii. We found that the occurrence of three scale types is likely to have been overlooked in the original descriptions of both P. sorokinii and C. birgeri. We also found that environmental metabarcodes identical to the sequence of RCC5270 were abundant in the location from which C. birgeri was initially described (Gulf of Finland). We conclude that P. sorokinii and C. birgeri are conspecific and P. sorokinii is therefore synonymous with C. birgeri. Based on its phylogenetic placement and nomenclatural priority we propose the new combination Pseudohaptolina birgeri and emend the description of this species.