Ulotrichophyceae

a class of multicellular green algae, with filamentous or lamellate thalli whose cells have one nucleus and, usually, one chloroplast. Asexual reproduction is through zoospores with four or, less commonly, two flagella or nonmotile spores. The sexual process is isogamy, heterogamy, or oogamy. The zygote develops into a resting spore or into a unicellular or multicellular sporophyte. The cycle of development is isomorphic or heteromorphic. Meiosis occurs with the zygote splitting into zoospores or with the zoospores (spores) forming in the thalli that develop from the zygotes. Depending on conditions, the gametophytes are capable of producing gametes or zoospores. The algae grow in fresh waters and in the sea; the most extensive genus is Ulothrix. Marine species include algae that live in limestone bottoms and in the shells of mollusks. Ulvaceous algae belong to Ulotrichophyceae.