Checklist of colourless euglenoids of the Czech Republic, with several taxonomic additions

This study presents the results of a complex survey of freshwater heterotrophic euglenoids in the Czech Republic, including both literature data and own field surveys of 469 sites visited in the course of three years. The checklist includes 189 taxa in 28 genera: Anisonema (10), Astasia (26), Atraktomonas (1), Calycimonas (2), Chasmostoma (1), Dinematomonas (3), Distigma (8), Dylakosoma (1), Entosiphon (4), Euglena (1), Gyropaigne (1), Heteronema (19), Jenningsia (11), Khawkinea (1), Lepocinclis (1), Menoidium (7), Neometanema (3), Notosolenus (18), Petalomonas (40), Phacus (1), Ploeotia (2), Pseudoperanema (7), Rhabdomonas (5), Scytomonas (1), Sphenomonas (5), Teloprocta (1) Tropidocyphus (1), Urceolus (4), and 4 species of uncertain identity. In addition, a general description of habitat types in which the taxa were found and a review of the current taxonomy and nomenclature of included taxa are provided. Several taxonomic and nomenclatural novelties are proposed, based on the review of morphological features, mostly applying to the genera Notosolenus and Jenningsia.

Molecular phylogenetics of sessile Dolium sedentarium, a petalomonad euglenid

The euglenids are a species-rich group of flagellates with varying modes of nutrition that can be found in diverse habitats. Phagotrophic members of this group gave rise to phototrophs and hold the key to understanding the evolution of euglenids as a whole, including the evolution of complex morphological characters like the euglenid pellicle. Yet to understand the evolution of these characters, a comprehensive sampling of molecular data is needed to correlate morphological and molecular data, and to estimate a basic phylogenetic backbone of the group. While the availability of SSU rDNA and, more recently, multigene data from phagotrophic euglenids has improved, several "orphan" taxa remain without any molecular data whatsoever. Dolium sedentarium is one such taxon: It is a rarely-observed phagotrophic euglenid that inhabits tropical benthic environments and is one of few known sessile euglenids. Based on morphological characters, it has been thought of as part of the earliest branch of euglenids, the Petalomonadida. We report the first molecular sequencing data for Dolium using single-cell transcriptomics, adding another small piece in the puzzle of euglenid evolution. Both SSU rDNA and multigene phylogenies confirm it as a solitary branch within Petalomonadida.

Phylogenomics of novel ploeotid taxa contribute to the backbone of the euglenid tree

Euglenids are a diverse group of flagellates that inhabit most environments and exhibit many different nutritional modes. The most prominent euglenids are phototrophs, but phagotrophs constitute the majority of phylogenetic diversity of euglenids. They are pivotal to our understanding of euglenid evolution, yet we are only starting to understand relationships amongst phagotrophs, with the backbone of the tree being most elusive. Ploeotids make up most of this backbone diversity-yet despite their morphological similarities, SSU rDNA analyses and multigene analyses show that they are non-monophyletic. As more ploeotid diversity is sampled, known taxa have coalesced into some subgroups (e.g. Alistosa), but the relationships amongst these are not always supported and some taxa remain unsampled for multigene phylogenetics. Here, we used light microscopy and single-cell transcriptomics to characterize five ploeotid euglenids and place them into a multigene phylogenetic framework. Our analyses place Decastava in Alistosa; while Hemiolia branches with Liburna, establishing the novel clade Karavia. We describe Hemiolia limna, a freshwater-dwelling species in an otherwise marine clade. Intriguingly, two undescribed ploeotids are found to occupy pivotal positions in the tree: Chelandium granulatum nov. gen. nov. sp. branches as sister to Olkasia, and Gaulosia striata nov. gen. nov. sp. remains an orphan taxon.

Multigene phylogenetics of euglenids based on single-cell transcriptomics of diverse phagotrophs

Euglenids are a well-known group of single-celled eukaryotes, with phototrophic, osmotrophic and phagotrophic members. Phagotrophs represent most of the phylogenetic diversity of euglenids, and gave rise to the phototrophs and osmotrophs, but their evolutionary relationships are poorly understood. Symbiontids, in contrast, are anaerobes that are alternatively inferred to be derived euglenids, or a separate euglenozoan group. Most phylogenetic studies of euglenids have examined the SSU rDNA only, which is often highly divergent. Also, many phagotrophic euglenids (and symbiontids) are uncultured, restricting collection of other molecular data. We generated transcriptome data for 28 taxa, mostly using a single-cell approach, and conducted the first multigene phylogenetic analyses of euglenids to include phagotrophs and symbiontids. Euglenids are recovered as monophyletic, with symbiontids forming an independent branch within Euglenozoa. Spirocuta, the clade of flexible euglenids that contains both the phototrophs (Euglenophyceae) and osmotrophs (Aphagea), is robustly resolved, with the ploeotid Olkasia as its sister group, forming the new taxon Olkaspira. Ploeotids are paraphyletic, although Ploeotiidae (represented by Ploeotia spp.), Lentomonas, and Keelungia form a robust clade (new taxon Alistosa). Petalomonadida branches robustly as sister to other euglenids in outgroup-rooted analyses. Within Spirocuta, Euglenophyceae is a robust clade that includes Rapaza, and Anisonemia is a well-supported monophyletic group containing Anisonemidae (Anisonema and Dinema spp.), 'Heteronema II' (represented by H. vittatum), and a clade of Neometanema plus Aphagea. Among 'peranemid' phagotrophs, Chasmostoma branches with included Urceolus, and Peranema with the undescribed 'Jenningsia II', while other relationships are weakly supported and consequently the closest sister group to Euglenophyceae remains unresolved. Our results are inconsistent with recent inferences that Entosiphon is the evolutionarily pivotal sister either to other euglenids, or to Spirocuta. At least three transitions between posterior and anterior flagellar gliding occurred in euglenids, with the phylogenetic positions and directions of those transitions remaining ambiguous.

The Molecular Diversity of Phagotrophic Euglenids Examined Using Single-cell Methods

Euglenids are a diverse group of euglenozoan flagellates that includes phototrophs, osmotrophs, and phagotrophs. Despite making up most of the phylogenetic diversity of euglenids, phagotrophs remain understudied, and recent work has focused on 'deep-branching' groups. Spirocuta is the large clade encompassing all flexible euglenids including the phototroph and primary osmotroph clades, plus various phagotrophs. Understanding the phylogenetic diversity of phagotrophic spirocutes is crucial for tracing euglenid evolution, including how phototrophs arose. We used single-cell approaches to greatly increase sampling of SSU rDNA for phagotrophic euglenids, particularly spirocutes, including the first sequences from Urceolus, Jenningsia, Chasmostoma, and Sphenomonas, and expanded coverage for Dinema and Heteronema sensu lato, amongst others. Urceolus monophyly is unconfirmed. Organisms referred to Jenningsia form two distinct clades. Heteronema vittatum and similar cells branch separately from Heteronema (c.f.) globuliferum and Teloprocta/Heteronema scaphurum, while Dinema appears as 2-3 clades. Sphenomonas is monophyletic and the deepest branch within Petalomonadida. The census of genera markedly underestimates the phylogenetic diversity of phagotrophs, but taxonomic restraint is necessary when sequences are not available from type species or reasonable surrogates. SSU rDNA phylogenies do not resolve most deep relationships within Spirocuta, but identify units of diversity to sample in future multigene analyses.

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.