The blastocladialeans are zoosporic fungi inhabiting freshwater or soil. They are saprobic or parasitic on algae, land plants, invertebrates and fungi. Some species are facultative anaerobes and grow under foul conditions.

Thalli are monocentric, polycentric or mycelial. Coelomomyces produces a tubular unwalled thallus in its host. Asexual reproduction by uniflagellate zoospores or spores. Sexual reproduction by isogamy to anisogamy. Some species show alternation between isomorphic gametophyte and sporophyte. Zoospore possesses a cone-shaped nucleus covered anteriorly by a membrane-bounded ribosomal cap (nuclear cap). The posterior part of the nucleus is surrounded by microtubules radiating from the basal body. There is no electron-opaque plug in the transitional region of flagellum. Centriole is arraanged in right angle to the basal body. There is a microbody-lipid globule complex. Golgi body lacks cisternal stacking except for Physoderma. Mitosis is closed without fenestrate pole.

The blastocladialean fungi were traditionally classified into the Chytridiomycota, but they have been transferred to new phylum because of phylogenetically distinctness.