Abstract
The areolae structure of Amphitetras antediluviana Ehrenberg growing profusely on sandy sediment in Toyama Bay was observed in detail using a scanning electron microscope. We found that there are two types of areolae occlusion within one valve. Many areolae were occluded by complex cribra near their outer openings. As each pore of the cribrum bears a flap on its outer surface, externally, many circular slits were observed in the occlusion. However, the meshwork of the cribrum was apparent, internally. The other areolae were occluded by volae with distinctive slits. Each vola was somewhat raised and located on the outer opening of the areola. The slits of the volae were also evident internally. The areolae with this occlusion were not abundant but were distributed over the valve, however, they were not observed at the circular elevated area of the valve.
