Ultrastructure of Allapsa vibrans and the body plan of Glissomonadida (Cercozoa).

Biciliate, gliding zooflagellate Cercozoa are globally the most abundant and genetically diverse predators in soil (glissomonads and cercomonads). We present the first detailed ultrastructural study of a phylogenetically well-characterized glissomonad, Allapsa vibrans. There are two ventral posterior centriolar roots as in Cercomonadida, but fewer other microtubular roots. Allapsa's centriolar roots and rhizoplast basically resemble those of the less well studied glissomonads Bodomorpha and Neoheteromita. The posterior centriole of Allapsa attaches laterally to the base of the anterior centriole and to the nucleus by striated fibrillar connectors and nests in a shallow cup-like ventrolateral depression; two broad fans of single microtubules line the cup's posterior and inner side. The anterior centriole has a dorsal two-microtubule root and probably also a singlet root. Its medium-length ciliary transition zones have a proximal hub-lattice and a prominent dense distal transverse plate/collar complex. Golgi bodies are anterior/paranuclear; isodiametric extrusomes are anterior mid-ventral. Tubulicristate mitochondria attach to the nucleus, as do prominent microbodies. We characterize the body plan of glissomonads, comparing it with other Sarcomonadea: their sister group (Pansomonadida) and the phylogenetically more distant Cercomonadida. We discuss glissomonad radiation into families Sandonidae, Proleptomonadidae, Dujardinidae, Bodomorphidae and Allapsidae, establishing Aurigamonadidae fam. n. for the amoeboflagellate pansomonad Aurigamonas.

Helkesimastix marina n. sp. (Cercozoa: Sainouroidea superfam. n.) a gliding zooflagellate of novel ultrastructure and unusual ciliary behaviour.

Unlike Helkesimastix faecicola and H. major, Helkesimastix marina is marine, ingests bacteria, is probably also a cannibal, and differs in cell cycle ciliary behaviour. Daughter kinetids have mirror symmetry; pre-division cilia beat asymmetrically. We sequenced its 18S rDNA and studied its ultrastructure to clarify its taxonomy. Helkesimastix (Helkesimastigidae fam. n.) differs unexpectedly radically from cercomonads, lacking their complex microtubular ciliary roots, grouping not with them but with Sainouridae within Pansomonadida. Longitudinal cortical microtubules emanate from a dense apical centrosomal plate, where a striated rhizoplast attaches the nucleus, and two very short subparallel centrioles attach by dense fibres. The marginally more posterior centriole, attached to the centrosomal plate by a dense forked fibre, bears the long 9+2 gliding posterior cilium and a microtubular root; the left-side, nucleus-attached, left centriole bears an immotile ciliary stump with abnormal axoneme of nine disorganized mainly singlet microtubules, unlike the sainourid anterior papilla. Both transitional regions have a proximal lattice, the posterior centriole with slender hub. Sainouroidea superfam. n. (Sainouridae; Helkesimastigidae) have homologous cytoskeletal geometry. Dorsal Golgi dictyosome and posterior microbody are attached to the nuclear envelope, which has slender micro-invaginations and probably a cortical lattice. Bacteria are digested posteriorly in association with numerous mitochondria with flat cristae.

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 approximately 80 degrees 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.

Morphology and phylogeny of Sainouron acronematica sp. n. and the ultrastructural unity of Cercozoa.

Sainouron are soil zooflagellates of obscure taxonomy. We studied the ultrastructure of S. acronematica sp. n. and sequenced its extremely divergent 18S rDNA and that of Cholamonas cyrtodiopsidis (here grouped as new family Sainouridae) to clarify their phylogeny. Ultrastructurally similar, they weakly group together, deeply within Monadofilosa. Sainouron has three cytoplasmic microtubules; all organelles specifically link to them or the nucleus. Mature centrioles have fibrous rhizoplasts. The posterior centriole bearing the motile cilium (with cortical filaments) has a transitional hub-lattice; a dense spiral fibre links its thicker rhizoplast and triplets; its ciliary root has two microtubules: mt1, underlying the plasma membrane, initiates at the spiral fibre; mt2, laterally attached to mt1 and nucleus, initiates in the amorphous centrosomal region. The anterior younger cilium, an immotile stub with submembrane skeleton as in Cholamonas, lacks axoneme, microtubular root, rhizoplasts and spiral fibre, but becomes the posterior one every cell cycle. The nuclear envelope donates coated vesicles directly to the Golgi, which makes kinetocyst-type extrusomes, concentrated at the cell anterior for extrusion into phagosomes. Ciliary transition region proximal hub-lattices (postulated to contain centrin) and distal nonagonal fibres are cercozoan synapomorphies, found with slight structural variation in all flagellate Cercozoa, but not in outgroups.