cryptomycota

…fungi (referred to as the cryptomycota), members of which average about 3 to 5 μm (1 μm is about 0.000039 inch) in length, have cell walls lacking chitin, and possess a flagellum. Phylogenetic analyses of ribosomal RNA in this clade suggest that it is an ancient fungal group.

In addition, the so-called cryptomycota, a primitive group of microscopic fungi, diverge significantly from the standard body plan of other fungi in that their cell walls lack the rigid polymer known as chitin. These microscopic fungi also possess a whiplike flagellum.