Abstract
The fine structure of the marine diatom species Achnanthes longipes is presented. The valve shape is panduriform to linear-lanceolate, with biseriate striae on both valves; the cells have many disc-shaped plastids. This species forms colonies of long chains, usually with more than 10 individuals connected to each other. However, these colonies are not formed by terminal spines or marginal ridges on the ARV. Japanese specimens possess terminal orbiculi. As terminal orbiculi may appear as one of the structural patterns of large and modified cribra, we suggest that both individuals those forming terminal orbiculi on the ARV and those lacking them are classified as A. longipes.
