Although various eukaryotic organisms, such as arthropods, endolichenic/lichenicolous fungi, and nematodes, have been isolated from lichens, the diversity and structure of eukaryotic communities associated with lichen thalli has not been well studied. In addressing this knowledge gap, we used bar-coded pyrosequencing of 18S rRNA genes to survey eukaryotes associated with thalli of three different lichen species. In addition to revealing an expected high abundance of lichen biont-related 18S genes, sequences recovered in our survey showed non-biont fungi from the Ascomycota also have a substantial presence in these thalli. Our samples additionally harboured fungi representing phyla (Blastocladiomycota, Chytridiomycota) that have not been isolated previously from lichens; however, their very low abundance indicates an incidental presence. The recovery of Alveolata, Metazoa, and Rhizaria sequences, along with recent work revealing the considerable bacterial diversity in these same samples, suggests lichens function as minute ecosystems in addition to being symbiotic organisms.