- umbilicata Quoy & Gaimard, 1833 = Eunaticina umbilicata (family Naticidae – Naticinae)
- umbilicatus Tenison Woods, 1876 = Muricopsis umbilicatus (family Muricidae – Muricopsinae)
- umbonella Lamarck, 1818 = Cyclotellina umbonella (family Tellinidae – Arcopagiinae)
- umbraculum Lightfoot, 1786 = Umbraculum umbraculum (family Umbraculidae)
- uncinata Quoy & Gaimard, 1824 = Onychoteuthis banksii (family Onychoteuthidae)
- undata Suter, 1913 = Anomia trigonopsis (family Anomiidae – Anomiinae)
- undatus Lamarck, 1816 = Clanculus undatus (family Trochidae – Trochinae)
- undulata Lamarck, 1804 = Amoria undulata (family Volutidae – Amoriinae)
- undulata Sowerby, 1849 = Cancellaria undulata (family Cancellariidae – Cancellariinae)
- undulatus Lightfoot, 1786 = Turbo undulatus (family Turbinidae – Turbininae)
- undulatus Perry, 1811 = Fusinus undulatus (family Fasciolariidae – Fusininae)
- undulatus Sowerby, 1842 (non Nilsson, 1827) = Mesopeplum anguineum (family Pectinidae – Chlamydinae)
- undulatus Sowerby, 1842 (non Nilsson, 1827) = Notochlamys hexactes (family Pectinidae – Chlamydinae)
- undulosa Lamarck, 1818 = Gomphina undulosa (family Veneridae – Tapetinae)
- unifasciata Gray, 1826 = Austrolittorina unifasciata (family Littorinidae – Littorininae)
- unilirata Tenison Woods, 1878 = Lironoba unilirata (family Rissoidae – Rissoinae)
- unisulcata Kobelt, 1892 = Pseudamycla miltostoma (family Columbellidae – Atiliinae)
- uschakovi Yakovleva, 1952 = Placiphorella atlantica (family Mopaliidae)
- ustulata Deshayes, 1857 = Duplicaria ustulata (family Terebridae – Terebrinae)
- ustulata Reeve, 1855 = Scutellastra peronii (family Patellidae)
- ustulata Sowerby, 1883 = Polinices conica (family Naticidae – Naticinae)
- ustulatus Reeve, 1847 = Fusinus undulatus (family Fasciolariidae – Fusininae)