AULACOSEIRA SATSUMAENSIS, A NEW PLIOCENE DIATOM SPECIES WITH TWO MORPHOTYPES FROM KAGOSHIMA, JAPAN

Abstract

Aulacoseira satsumaensis H. Tanaka sp. nov., is described from a Pliocene freshwater sediment of the Koriyama Formation in Kagoshima Prefecture, Kyushu, Japan. The species is characterized by having different valve morphology between thick wall valves and thin wall valves. The thick wall valves, including the initial cell, have a larger diameter, a shorter mantle, fewer punctae rows and coarser punctae in the rows than the latter. Also, the thick wall morphotype has very thick transverse costae on the inner mantle wall while the thin wall morphotype exhibit thick pervalver costae. Another difference between the two morphotypes is in the location of their rimoportulae. This new species is compared to three other similar Aulacoseira species, A. krammeri R.K. Edgar, Kociolek & S.M. Edgar, reported from Miocene deposits in Oregon, USA, and described as having robust and gracile morphotypes, A. nipponica (Skvortsov) Tuji, originally described from Lake Biwa, Japan and A. sp., reported from a Pliocene deposit of Kyushu, Japan, the same island as A. satsumaensis was found.