- Uncinulus, genus
- undulata, Paphia
- undulata, Paratapes
- Undulate venus
- undulatum, Lithophyllon
- undulatus, Actinocyclus
- undulatus, Actinoptychus
- ungeri, Planera
- ungeri, Zelkova
- ungius, Lingula
- unguiculatus, Mytilus
- unicarinata, Iphinoe
- unicarinata, Neoiphinoe
- unicarinata, Trichotropis
- Unio, genus
- Unio douglasiae ssp. biwae
- Unionid
- Unionidae, family
- Unionites, genus
- Unionites carinatus
- Unio uryuensis
- universa, Orbulina
- unumaense, Eucyrtidiellum
- ushimarensis, Equisetites
- ushioi, Minetaxites
- ussuricus, Entolium
- ussuricus, Eupecten
- ussuricus, Pecten
- ussuricus, Pecten (Eupecten)
- usta, Diplodonta
- usta, Felaniella
- usyuensis, Alnus
- usyuensis, Rosa