Reminiscent of the pre-diatom? A hitherto undescribed scaly bolidophyte Lepidoparma frigida gen. et sp. nov. in a new order Lepidoparmales based on morphology, phylogeny, and ecology.

The class Bolidophyceae, which consists of small phytoplankton distributed worldwide, is the sister group of diatoms. This class has contained only one order, the Parmales, until now. In this study, we established a new order Lepidoparmales Kamakura & S.Sato ord. nov. and a new family Lepidoparmaceae Kamakura & S.Sato fam. nov., within the Bolidophyceae, and described Lepidoparma frigida Kamakura & S.Sato gen. et sp. nov. from the Sea of Okhotsk. We conducted a comprehensive comparison of L. frigida with diatoms and other parmaleans through analysis of its molecular phylogeny, morphology, ultrastructure, ontogeny, distribution, and lipid composition. The cell surface of L. frigida is covered with numerous siliceous scales with radial patterns similar to centric diatom valves; this character distinguishes it from other known parmaleans. Intriguingly, its appearance resembles the hypothesized "pre-diatom," which was proposed to be a precursor to primitive diatoms. The discovery and characterization of L. frigida will provide valuable insights into the evolutionary processes of both diatoms and bolidophytes and shed light on their common ancestor.