Foraminifera Fauna in the Core Sediments of the Ulleung Basin, East Sea (Sea of Japan) of Republic of Korea

Foraminifera are unicellular protists with external shells (tests) that may be calcareous (porcelaneous or hyaline), agglutinated, or organic-walled. Their test morphology and as-assemblage composition closely track environmental forcing, making them robust bioindicators of marine change. Documenting morphology and faunal composition is therefore essential for interpreting species distributions and their paleoenvironmental significance. Here we provide a systematic account of foraminiferal assemblages from core sediments in the Ulleung Basin, East Sea (Sea of Japan), with accompanying imagery and diagnostic notes. We identify 47 species across 32 genera and 20 families, including 15 planktic and 32 benthic taxa. Seven species are newly recorded for Korean waters: the planktic Tenuitellita fleisheri and Neogloboquadrina atlantica subsp. praeatlantica, and the benthic Islandiella algida, Uvigerina asperula, Pseudonodosaria aequalis, Pseudonodosaria obtusissima, and Astacolus crepidula. The presence of these previously unreported taxa likely reflects historical under-sampling and limited taxonomic emphasis in the region, coupled with the geomorphological challenges of the Ulleung Basin. In addition, the recognition of five distinct morphotypes of Neogloboquadrina pachyderma points to substantial past environmental variability in the basin. Continued evaluation of morphological diversity and distributional patterns in these assemblages will support stratigraphic applications and reconstruction of past marine environments in the East Sea by clarifying depth-wise faunal turnovers that likely record a composite signal of hydrographic variability overprinted by episodic seismic disturbance and slope current reworking.