Planomonadida ord. nov. (Apusozoa): Ultrastructural Affinity with Micronuclearia podoventralis and Deep Divergences within Planomonas gen. nov.

Gliding zooflagellates previously misidentified as Ancyromonas sigmoides, Metopion or Heteromita constitute a new genus Planomonas. Three new Planomonas species (marine P. micra and P. mylnikovi: freshwater P. limna) have extremely divergent 18S rRNA and subtly but consistently different light microscopic morphology, distinguishable from P. (=Ancyromonas) melba comb. nov. and P. (=Bodo) cephalopora comb. nov. Ultrastructurally, P. micra and P. mylnikovi have a sub-plasma membrane dense pellicular layer (except in the ventral feeding pocket whose rim is supported by microtubules), kinetocysts, and flat mitochondrial cristae. Centrioles, connected at ∼80° by short fibres, have a dense amorphous distal plate below a double axosome and four microtubular roots. Microbody, mitochondrion, and dictyosomes associate with the nucleus. Longitudinal cytokinesis is slow and peculiar; ciliary transformation is from anterior to posterior as in other bikonts. Planomonads, like the non-flagellate Micronuclearia (here grouped with planomonads as Hilomonadea cl. nov.), have an indistinguishable single dense pellicular layer, not a double layer like apusomonads (comprising emended class Thecomonadea, phylum Apusozoa). We also sequenced 18S rDNA for Planomonas howeae sp. nov. and Micronuclearia podoventralis, plus actin genes of P. micra, Micronuclearia, Amastigmonas marina. All were analysed phylogenetically; the Planomonas clade is ancient, diverse and robust: it sometimes groups weakly as sister to Micronuclearia.