A Deeply Branching Lineage in Heterolobosea (Discoba) With Multiflagellated and Multigrooved Life Stages

ABSTRACT

Several distantly related, deep‐branching lineages within the eukaryotic tree of life share what is known as the “typical excavate” morphology. This cell architecture includes a suspension‐feeding ventral groove, supported by complex and specific structures of the cytoskeleton, and a vane‐bearing posterior flagellum. Within Discoba, such characteristics were found only in the deepest branch, Jakobida, also famous for having the most gene‐rich and bacterial‐like mitogenomes. Some members of the discoban lineage Heterolobosea also possess a ventral groove. However, they lost many other typical excavate characteristics, including the flagellar vane and some flagellar root elements. We have established a clonal culture of a free‐living freshwater flagellate from Malaysia, strain NY0229, described here under the provisional name Multisulcus malaysiensis nom. prov. Electron microscopy observations show a conspicuous ventral groove reinforced with microtubules of the flagellar apparatus and a vane on the posterior flagellum. Strain NY0229 has typical excavate biflagellated forms but also exhibits very atypical multiflagellated and multigrooved forms. The kinetid consists of two orthogonally oriented kinetosomes; both flagella of biflagellate cells display proximal and distal projections. Molecular phylogenetic analyses support a deep‐branching position of the new strain within Heterolobosea, as the sister lineage to all previously known Eutetramitia.