Uncovering a new Scrippsiella species from the Black Sea: Scrippsiella phycobiana sp. nov. (Thoracosphaerales, Dinophyceae)

SUMMARY The dinophyte genus Scrippsiella is a common and ecologically important component of coastal microplankton communities, yet its species diversity in the Black Sea remains insufficiently resolved due to morphological similarity among taxa and the scarcity of integrative taxonomic studies. Here, we describe Scrippsiella phycobiana sp. nov., a new species isolated from plankton samples collected during a 2021 survey in the western Black Sea. The species was characterized using a combination of light and scanning electron microscopy, cyst observations, and molecular phylogenetic analyses based on sequences from the SSU rDNA, LSU rDNA, and ITS regions. Motile cells are ellipsoid and morphologically similar to other congeners, but the species is distinguished by a unique thecal plate pattern with only two anterior intercalary plates, interpreted as a fusion of plates 2a and 3a – an apomorphic feature not previously documented in the genus. Calcareous cysts are spherical with short processes and a round archeopyle. Phylogenetic analyses of concatenated ITS–LSU sequences place S. phycobiana in a well‐supported clade within the S. trochoidea species complex, indicating a distinct evolutionary lineage closely related to strains tentatively identified as S. trochoidea or S. cf. erinacea . The discovery of S. phycobiana highlights previously unrecognized diversity within Black Sea Scrippsiella populations and supports the hypothesis that records attributed to S. acuminata represent multiple cryptic lineages. Our results emphasize the necessity of strain‐based integrative taxonomy for accurate species delimitation in morphologically conservative dinoflagellates and provide a framework for future biogeographic and ecological investigations of the genus.