1. Ulvaceae J.V. Lamouroux ex Dumortier 1822
2. Unionidae Rafinesque 1820
3. Upogebiidae Borradaile 1903
4. Uranoscopidae Jordan & Evermann 1898
5. Urolophidae J.P. Müller & Henle 1841
6. Ursidae G. Fischer de Waldheim 1817