- Turborotalita quinqueloba
- Turritopsis nutricula
- Tuscarantha braueri
- Tuscarantha hydra
- Tuscarantha luciae
- Tuscaretta aeronauta
- Tuscaretta globosa
- Tuscaretta tubulosa
- Tuscarilla ampulla
- Tuscarilla campanella
- Tuscarilla nationalis
- Tuscarilla similis
- Tuscarora bisternaria
- Typhloscolex mulleri
- Uca burgersi
- Uca cumulanta
- Uca leptodactyla
- Uca maracoani
- Uca mordax
- Uca rapax
- Uca thayeri
- Uca uruguayensis
- Uca victoriana
- Uca vocator
- Ucides cordatus
- Undella claparedei-group
- Undella grandis
- Undella hemisphaerica
- Undella hyalina
- Undellopsis marsupialis
- Undeuchaeta incisa
- Undeuchaeta major
- Undeuchaeta plumosa
- Undinula vulgaris
- Uronema marinum
- Uronychia transfuga
- Valdiviella brevicornis
- Valdiviella insignis
- Valdiviella minor
- Valdiviella oligarthra
- Vallentinia falklandica
- Vallentinia gabriellae
- Vampyroteuthis infernalis
- Vanadis antarctica
- Vanadis crystallina
- Vanadis formosa
- Vanadis longissima
- Vanadis minuta
- Vanadis studeri
- Vanadis tagensis