An Amoeboflagellate Halosymphonia sogumizoara gen. et sp. nov . ( T ulamoebidae) in Heterolobosea Enhances the Core Halophilic Radiation of Eukaryotes

Most known halophilic and halotolerant eukaryotes belong to the taxon Heterolobosea sensu lato. Within this group, the Tulamoebidae-Aurem clade comprises exclusively halophiles, supporting the hypothesis that this clade represents an adaptive radiation of halophilic eukaryotes. In this study, we describe a novel amoeboflagellate, strain TA, isolated from a sample with a salinity level of 200 practical salinity units (PSU). Morphological and molecular analyses indicate that strain TA belongs to the Heterolobosea, forming a sister lineage to Aurem hypersalina and clustering with Tulamoebidae. The amoeboid stage exhibits a monopodial limax form with eruptive movement and numerous inclusions, whereas the flagellate form differs distinctly from that of A. hypersalina, exhibiting homodynamic flagella beating. Strain TA grows optimally at 100-150 PSU. We designate it as Halosymphonia sogumizoara gen. nov., et sp. nov., and expand the Tulamoebidae by including Halosymphonia together with Aurem. Based on our qualitative estimation, H. sogumizoara displayed a steady increase in intracellular Na⁺ concentration with increasing salinity (100-200 PSU), while K⁺ levels remained relatively stable, suggesting a primarily salt-out strategy. Therefore, Tulamoebidae represents a core halophilic eukaryotic clade for comparative evolutionary and physiological studies with halophilic prokaryotes.