COMPARATIVE-STUDIES AMONG 4 LINEAR-LANCEOLATE ACHNANTHIDIUM SPECIES (BACILLARIOPHYCEAE) WITH CURVED TERMINAL RAPHE ENDINGS

In Japan there are four Achnanthidium taxa resembling each other in ha ving a raphe with curved terminal endings. They occur in oligotrophic zones of streams, mostly in the upper part, and are ecologically impor tant. All available characteristics, such as valve shape, axial area, hyaline areas at the juncture of valve face and mantle, striae arrange ment on the valve face, shape of the terminal raphe endings and centra l raphe endings, structure of the areolae forming the striae, arrangem ent of the mantle areolae on both sides and ends of the valve, examine d by LM and SEM, were used for comparison. Achnanthidium latecephalum spec. nov. is described. At the same time the already known species Ac hnanthes pyrenaica, A. japonica and A. convergens are transferred to t he genus Achnanthidium.