New data on the morphology, taxonomy, ecology, and distribution of Stephanodiscus agassizensis HAyenkansson et Hickel (Bacillariophyta)

The study of samples from various waterbodies (rivers, lakes, reservoirs, and seas) has shown that S. agassizensis manifests a significant morphological variability of qualitative and quantitative characters (the valve diameter and its relief, the mantle height, and the presence and arrangement valve face fultoportulae) which distinguish this species from other species with similar a morphology (S. neoastraea, S. heterostylus, S. alpinus, and S. maximus). Original and literature data on the morphology, ecology, and distribution of S. agassizensis has allowed the author to specify its taxonomic position, refer the species to the synonymy of S. neoastraea, and extend the diagnosis of the latter.