Fornicata is a recently (Simpson 2003) recognized clade that belongs to the eukaryotic supergroup Excavata. Fornicates are unicellular heterotrophic flagellates with one or two karyomastigonts per cell. One karyomastigont bears one to four flagella. Fornicates exhibit several unusual characteristics, notably absence of classical mitochondria. Therefore, they were once considered to represent basal, primarily amitochondriate eukaryotes, so-called “Archezoa”. However, it has been shown that the presumably primitive fornicate cell arose rather by simplification and that Fornicata possess reduced mitochondria-related organelles.

The clade consists of four disparate lineages: free-living Carpediemonas and Dysnectes, both free-living and parasitic diplomonads (Diplomonadida), and almost exclusively parasitic retortamonads (Retortamonadida). Diplomonads, the best known fornicate group, comprise several important parasitic species including the human intestinal pathogen Giardia intestinalis. Interestingly, most diplomonads are diplozoic, i.e. their cells possess two identical and axially symmetrical sets of all cellular structures, though the symmetry is probably only superficial. Some diplomonads also use an alternative genetic code. The other fornicates, i.e. retortamonads, Carpediemonas and Dysnectes, are among the least studied eukaryotes.