MORPHOLOGY AND TAXONOMY OF THE CENTRIC DIATOM CYCLOTELLA-ATOMUS

The type material as well as raw material from the type locality of Cy clotella atomus from Java (Hustedt Collection), material from the rive r Wumme (Hustedt Collection) and recent material from rivers in Englan d were examined. Light and electron microscopic investigation revealed only minor morphological differences. The structure of the central ar ea of the valve face, the number of valve face fultoportulae and the n umber of satellite pores of the mantle fultoportulae were constant. Bo th valve shape and the number of satellite pores (2 or 3) on the valve face fultoportula can vary. Contrary to the findings of other workers the orientation of the labium of the rimoportula is independent of th e number of the satellite pores of the valve face fultoportula. Ecolog ical studies suggest that C. atomus is a cosmopolitan, fresh- to brack ish water species and is one of the diatoms which can withstand turbul ence and tolerate periodic osmotic stress.