A mesokaryote or mesokaryotic organism is a single-celled eukaryote that shows intermediate resemblance to both prokaryotes and 'higher' eukaryotes. The term originates from a 1965 hypothesis by John David Dodge, who proposed that certain eukaryotes (mainly dinoflagellates) with closed mitosis and other traits considered 'primitive' were an intermediate step between prokaryotes and the remaining eukaryotes. This idea originated in the late 20th century, and was later disproven by more detailed ultrastructural studies in the following decades.