unitunicate ascus (adjective,ascus term; synonym: non-fissitunicate) – with a single functional layer; referring to asci that are not separating into endo- and exoascus during spore discharge; usually thin-walled and somewhat elongated. Early studies suggested that unitunicate asci were one of two fundamentally different types (unitunicate and bitunicate). Ultrastructural examination later revealed that unitunicate asci have several ultrastructural ascus wall layers. In early classification systems ascomycetes with bitunicate asci where generally believed to have an ascohymenial ontogeny and were referred to as Hymenoascomycetes = Ascohymeniales = Unitunicatae. Kind of:ascus dehiscence type.