Lotharella oceanica sp. nov. - A new planktonic chlorarachniophyte studied by light and electron microscopy

A new chlorarachniophyte alga, Lotharella oceanica sp. nov., is described. This alga is the fifth named species in the genus Lotharella and has naked (wall-less) spherical cells as its vegetative stage. Swimming cells (zoospores) with a single flagellum were also observed in the organism's life cycle, although cell division appears not to occur in the swimming stage. Lotharella oceanica was collected and isolated from open ocean water in the Sargasso Sea and maintained as strain CCMP622 at the Provasoli-Guillard National Center for Culture of Marine Phytoplankton, the Bigelow Laboratory for Ocean Sciences, USA. CCMP622 was originally described as a strain of Bigelowiella natans, one of the planktonic chlorarachniophytes. However, the original description of B. natans clearly showed that this isolate (strain CCMP622) possesses a deep-slit type of pyrenoid, which is a diagnostic character for members of the genus Lotharella, Moreover, in a previously published phylogenetic study of the chlorarachniophytes including CCMP622, it was suggested that this strain could represent a new species of Lotharella; its taxonomy thus became uncertain. We have studied the morphology, life cycle and ultrastructure of strain CCMP622 to clarify its taxonomie position and demonstrate that this isolate does not belong to the genus Bigelowiella but rather belongs to Lotharella. We thus describe it as Lotharella oceanica sp. nov.