The fine structure of Cyclotella rhomboideo-elliptica Skuja, from a Middle Pleistocene Deposit, Gunma Prefecture, Central Japan

Abstract

The fine structure of Cyclotella rhomboideo-elliptica Skuja was examined using light and scanning electron microscopy. Plenty of frustules of this species which are described here were taken from a diatomite layer that was inserted in the Upper Nakanojo Lacustrine Deposit (Middle Pleistocene) which is assumed to be from about 0.3 to 0.5million years old, middle Pleistocene, Central Japan.
This species is characterized strongly by its asymmetrically distorted frustules. The frustules are parallelogram-shaped in the girdle view and from rhomboidal to elliptical in the valve view. The central part of the valve is externally reticulate-verrucose and prominently undulated.