An account of biological and evolutionary aspects of the Devonian microfossil Eovolvox Kaźmierczak and the related Precambrian Eosphaera Barghoorn is presented. New data are included confirming the volvocacean affinity of both microorganisms along with an interpretation of reproductive cycle in the Devonian Eovolvox. A critical review of other volvocalean-like microfossils is also provided. Evolutionary trends in coenobial/colonial Volvocales are discussed. Comparative features of Eovolvox and Eosphaera are summarized and comments are made to the problem of the oldest eukaryotes. The significance of Eosphaera-like protovolvocaceans as real phyletic archetypes for early metazoans is disputed.

Key words: Volvocaceae (Phytomonadina), morphology, evolution, Devonian, Precambrian.