Ploeotids Represent Much of the Phylogenetic Diversity of Euglenids

Ploeotids are an assemblage of rigid phagotrophic euglenids that have 10-12 pellicular strips and glide on their posterior flagellum. Molecular phylogenies place them as a poorly resolved, likely paraphyletic assemblage outside the Spirocuta clade of flexible euglenids, which includes the well-known phototrophs and primary osmotrophs. Here, we report SSU rRNA gene sequences from 38 ploeotids, using both single-cell and culture-based methods. Several contain group I or non-canonical introns. Our phylogenetic analyses place ploeotids in 8 distinct clades: Olkasia n. gen., Hemiolia n. gen., Liburna n. gen., Lentomonas, Decastava, Keelungia, Ploeotiidae, and Entosiphon. Ploeotia vitrea, the type of Ploeotia, is closely related to P. oblonga and Serpenomonas costata, but not to Lentomonas. Ploeotia cf. vitrea sensu Lax and Simpson 2013 is not related to P. vitrea and has a different pellicle strip architecture (as imaged by scanning electron microscopy): it instead represents a novel genus and species, Olkasia polycarbonata. We also describe new genera, Hemiolia and Liburna, for the morphospecies Anisonema trepidum and A. glaciale. A recent system proposing 13 suprafamilial taxa that include ploeotids is not supported by our phylogenies. The exact relationships between ploeotid groups remain unresolved and multigene phylogenetics or phylogenomics are needed to address this uncertainty.