THREE NEW SPECIES IN THE THALASSIOSIRA TRIFULTA GROUP IN LATE NEOGENE SEDIMENTS FROM THE NORTHWEST PACIFIC OCEAN

Abstract

Three new species in the Thalassiosira trifulta group are described from the Pliocene and Pleistocene sediments of the northwest Pacific Ocean: T. bipora Shiono, T. centra Shiono, and T. depressa Shiono. All possess one fultoportula and at least one small, pore-like structure at the valve centre. The latter structure is designated here as an occluded areola and is morphologically similar to a central fultoportula or a small areola. The new species are referred to the Thalassiosira bipora subgroup because they possess this occluded areola.