Morphology, phylogeny, and feeding behaviors of four unrecorded heterotrophic nanoflagellates from Korea

Abstract

Heterotrophic nanoflagellates (HNFs; 2–20 µm) play a key ecological role in marine microbial food webs as primary bacterivores that regulate bacterial populations and transfer carbon to higher trophic levels. However, the diversity and taxonomic information of marine HNFs in Korean coastal seawaters remain limited. Four HNF strains were isolated from surface seawater and sediment samples collected from Korean coastal areas. Morphological observations and 18S rDNA phylogenetic analyses identified the isolates as Fabomonas tropica in Ancyromonadida, Manchomonas bermudensis in Apusomonadida, Pimpavicka limacoides in Parabasalia, and Subulatomonas tetraspora in Breviatea, all newly recorded in Korea. All four strains fed on bacteria while attached to the substrate but exhibited distinct feeding strategies. Fabomonas tropica showed raptorial feeding using a feeding groove, M. bermudensis and S. tetraspora performed pseudopodial grasping feeding, and P. limacoides generated localized water currents with three anterior flagella to capture suspended prey. This study provides an integrative morphological, molecular, and behavioral characterizations of marine HNFs isolated from Korean coastal waters, contributing to their taxonomic identification and ecological understanding. The discovery of these species expands the known biogeographic distributions of Ancyromonadida, Apusomonadida, Parabasalia, and Breviatea. Furthermore, diverse feeding strategies may suggest differences in bacterial feeding rates in coastal ecosystems. © 2026 The Author(s).