Scanning electron microscopy and comparative micromorphology of the periplast ofHemiselmis rufescens, Chroomonassp.,Chroomonas salinaand members of the genusCryptomonas(Cryptophyceae)

Abstract

Scanning electron microscopy demonstrated small numbers of longitudinal offset rows of rectangular plates in Hemiselmis rufescens Parke and Chroomonas sp. Chroomonas salina Butcher and all examined strains of Cryptomonas showed numerous rows of smaller hexagonal plates. Regular arrays of peripheral trichocysts are absent in H. rufescens and account for the smooth appearance of the cell surface. In all other described members of the Cryptophyceae two trichocysts, one beneath each corner, are typically associated with the anterior facing edges of each plate. The subapical tubular gullet of the genera Chroomonas and Cryptomonas is absent in H. rufescens where the corresponding region is marked by an oval area without plates and a slightly raised posterior rim. The two anteriorly directed flagella emerge from beneath this rim or the sac-like invagination in Chroomonas and Cryptomonas. Sections of the periplast of H. rufescens and Chroomonas sp. showed the limiting plasma membrane sandwiched between an inner and outer plate component with additional fibrous material attached on the cell surface of Chroomonas sp. In Cryptomonas strains and Chroomonas salina the inner plate components are the only supporting structures of the periplast and variable amounts of fibrillar material is attached to the plasma membrane. The fundamental identity of the described periplast patterns and the systematic value of the observed differences were suggested.