The opisthokonts are one of the major super groups of eukaryotes. It comprises two major clades: (i) Holozoa, which includes Metazoa and its unicellular relatives (choanoflagellates, ichthyosporeans, and filastereans), and (ii) Holomycota, which includes Fungi and their unicellular relatives (nucleariids and rozellids). Here we investigated opisthokont diversity in freshwater and marine sediments using 18S rDNA sequencing.