In 1971, the algal class Eustigmatophyceae, Stramenopiles, was detached by Hibberd and Leedale from the class Xanthophyceae, Stramenopiles, on the basis of prominent ultrastructural differences in vegetative cells and more importantly in zoospores, such as the presence of big extraplastidial stigma. The class was divided into four families, six genera and twelve species. It seems so far, that there is a deep dichotomy within the class. Eliáš et al. (unpublished) recom- mend to establish two orders based on molecular sequencing of 18S rDNA and rbcL: Eustigmatales (sen- su Eustigmatophyceae described by Hibberd) and Goniochloridales (order containing Goniochloris, Pseu- dostaurastrum and undescribed relatives). The order Eustigmatales is divided into three separate lineages, most likely families: Eustigmataceae (A1), Monodopsidaceae (A2) and a new family Pseudellipsoidiona- ceae (A3). In this study the ultrastructure of 10 eustigmatophycean strains from three separate lineages was investigated. The typical characteristics of this class as chloroplast without a girdle lamella, a reddish glo- bule and lamellate vesicles were found in all strains studied. The appearance of the lamellate vesicles was found to change during the life cycle. My research indicates that other characteristics, formerly...