Cultivation and Characterisation of New Species of Apusomonads (the Sister Group to Opisthokonts), Including Close Relatives of Thecamonas (Chelonemonas n. gen.).

ABSTRACT

Apusomonads comprise an understudied and undersampled group of heterotrophic flagellates that is closely related to opisthokonts, the supergroup containing animals and fungi. We cultured representatives of a new clade of apusomonads, Chelonemonas n. gen., which is sister to marine forms of Thecamonas in SSU rRNA gene phylogenies. Scanning electron microscopy shows that members of Chelonemonas have a hexagonal patterning to their submembranous pellicle, which is not known to exist in other apusomonads. We propose that the subfamily Thecamonadinae refer to the marine Thecamonas/Chelonomonas clade. We also report two new strains of Multimonas, one of which is genetically divergent from previously described strains, and here described as a new species, Multimonas koreensis. Both strains of Multimonas have appendages on their dorsal surface that could be extrusomes, and a frilled appearance to the border of their pellicle. Explorations of taxon sampling in SSU rRNA gene phylogenies confirm the new strains' evolutionary affinities, but do not resolve relationships among the five main apusomonad clades. These phylogenies also separate the freshwater species "Thecamonas" oxoniensis from the marine members of the genus Thecamonas. The new strains described here may provide valuable genetic and morphological data for evaluating the relationships and evolution of apusomonads.