# Distribution and Feeding of Hexatilemonas jangsaensis, a Novel Cosmopolitan Member of the Uncultured Marine Apusomonad Clade

## TL;DR

Scientists discovered a new marine microorganism, Hexatilemonas jangsaensis, which feeds on bacteria and is found worldwide in ocean waters.

## Contribution

The study introduces a new marine apusomonad species and reveals its global distribution and feeding behavior.

## Key findings

- Hexatilemonas jangsaensis captures bacteria using lateral pseudopodia in a sit-and-wait feeding strategy.
- Hexatilemonas-like sequences are found in 29.2% of surface and 47.7% of deeper ocean samples globally.
- The new species belongs to an uncultured marine APU-30 clade and expands known apusomonad diversity.

## Abstract

The perplexing apusomonads, a sister lineage to Opisthokonta (including animals and fungi), are bacterivorous heterotrophic nanoflagellates whose diversity and ecological role remain poorly understood. Members of the large APU‐30 clade are found exclusively in marine environments and mostly comprise uncultured lineages. Here, we isolated a novel lineage within an uncultured subclade of APU‐30 from Korean coastal waters. Although the new isolate shares key morphological features with Chelonemonas in APU‐30, it possesses a differently segmented dorsal pellicle. Phylogenetic analyses placed this organism closest to the genetically distinct ‘Thecamonas’ sp. Bamfield. Based on a combination of morphological and genetic features, we propose a novel genus and species for this organism: Hexatilemonas jangsaenesis gen. et sp. n. This novel apusomonad captures bacteria with its lateral pseudopodia, showing a sit‐and‐wait feeding strategy, which probably provides an efficient way for utilising bacterial assemblages. Interestingly, environmental DNA surveys showed a widespread distribution of Hexatilemonas‐like sequences across global marine environments, occurring in 29.2% of epipelagic and 47.7% of mesopelagic samples, suggesting that this genus is cosmopolitan. Our findings expand the known diversity of apusomonads by describing a novel lineage and provide insights into previously uncharacterised lineages and their ecological roles in marine ecosystems.

This study describes a novel species of marine heterotrophic nanoflagellate, Hexatilemonas jangsaensis gen. et sp. n., within the uncultured APU‐30 clade, and highlights the global distribution pattern of this previously uncharacterised genus. This isolate is hypothesised to feed on bacteria attached to substrates in the water column using pseudopodia. It shows higher relative abundance in epipelagic depths than in mesopelagic depths and represents a cosmopolitan genus.