Diversity of Amphidomataceae (Dinophyceae) in the Black Sea, including description of Amphidoma pontica sp. nov.

SUMMARY The dinoflagellate family Amphidomataceae includes the genera Azadinium and Amphidoma , several species of which are known producers of lipophilic toxins known as azaspiracids (AZAs). However, the diversity, abundance, and distribution of this important group of nanoplanktonic dinoflagellates in the Black Sea remain poorly understood. To address this knowledge gap, Amphidomataceae were specifically investigated during a PHYCOB research cruise in the western Black Sea in September 2021. The study employed live microscopy observations on board, electron microscopy of field‐collected samples, quantitative assessments of abundance and distribution in preserved samples, and the establishment of clonal strains. Amphidomataceae species were detected at all stations, with abundances ranging from 1.2 to 13.0 × 10 3 cells per liter. However, no AZAs were detected in any of the field samples. Light microscopy and subsequent SEM analyses revealed a high diversity of species. Field‐sample‐SEM‐documented records included Azadinium trinitatum , Az. spinosum , Az. luciferelloides , an undescribed Azadinium species, Amphidoma languida , and an undescribed species of Amphidoma . Additionally, two clonal strains were successfully established and are newly described here as Amphidoma pontica . This new species closely resembles Am. languida and Am. fulgens , but is distinguished by the absence of contact between the distalmost apical plate (6′) and the distalmost precingular plate (6″). Molecular phylogenetic analysis based on concatenated ribosomal markers supports its classification as a distinct species. Neither of the Am. pontica strains produced detectable levels of AZAs. This study significantly contributes to a foundational assessment of the species diversity, distribution, and potential toxicity of Amphidomataceae in the Black Sea.