Paralia kawasumii sp. nov., a new fossil Paralia species with an elliptical valve from upper Holocene coastal sediments of the central Ise Plain, central Japan

A new fossil diatom species, Paralia kawasumii Sato sp. nov., has been found in upper Holocene coastal sediments of the central Ise Plain, central Japan. Detailed examination by light and scanning electron microscopy showed that P. kawasumii is a straight, chain-forming diatom characterized by double heterovalvy and spathulate linking spines. Like P. elliptica Garcia, its valve face is elliptical and undulate, and parallel and anastomosing ridges and grooves are present on sibling valve faces. Both species together comprise the ‘Paralia elliptica group’. However, P. kawasumii is considered a separate species from P. elliptica because of morphological differences in the structure and position of the rimoportulae and in the densities of fenestrae and of slits on the cingulum. Rimoportulae of P. kawasumii are perpendicular to the striae and distributed just below the overhanging mantle edge. Fenestrae and slits on the cingulum of P. kawasumii are more densely distributed than in P. elliptica. Paralia kawasumii is associated with loose sandy bottoms in intertidal areas (tidal flats to shallow outer bay environments). It is possible that P. kawasumii is an extant species, although no living cells have been found in surface sediments in Japan. If this were the case, P. kawasumii would be the fifth extant Paralia species in Japan.