ULTRASTRUCTURE OF 4 SPECIES OF THE DIATOM GENUS COCCONEIS WITH THE DESCRIPTION OF COCCONEIS-PSEUDOCOSTATA SPEC NOV

Light, scanning and transmission electron microscopy observations on t he structure of four species of the diatom genus Cocconeis are present ed here. The studied diatoms were collected in the southeast Pacific O cean from coastal waters, including some Chilean rivers estuaries and one freshwater lagoon, and from the Antarctic. The ultrastructural inf ormation obtained has revealed some features not previously recorded i n Cocconeis and allows us to relate structurally C. stauroneiformis, C . pseudocostata spec. nov. and C. fasciolata. Comparison of C. stauron eiformis and C. scutellum var. scutellum shows important ultrastructur al differences. Stria structure of the sternum valve (or araphid valve ) herein described for C. stauroneiformis and C. pseudocostata spec. n ov. is the most complex among those recognized up to now in Cocconeis valves.