The molecular diversity of phagotrophic Euglenids examined using single-cell methods

<p>Euglenids are a diverse group of euglenozoan flagellates that includes phototrophs, osmotrophs, andphagotrophs. 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 <em>Urceolus, Jenningsia, Chasmostoma</em>, and <em>Sphenomonas</em>, and expanded coverage for <em>Dinema</em> and <em>Heteronema</em> sensu lato, amongst others. <em>Urceolus</em> monophyly is unconfirmed. Organisms referred to Jenningsia form two distinct clades. <em>Heteronema vittatum</em> and similar cells branch separately from <em>Heteronema</em> (c.f.) <em>globuliferum</em> and <em>Teloprocta/Heteronema scaphurum</em>, while <em>Dinema</em> appears as 2–3 clades. <em>Sphenomonas</em> 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.</p>