- Tethys - (Greek mythology) a Titaness and sea goddess; wife of Oceanus
--1 is a kind of Titaness
- Aplysia, genus Aplysia, Tethys, genus Tethus - type genus of the family Aplysiidae
--2 is a kind of mollusk genus
--2 is a member of Aplysiidae, family Aplysiidae, Tethyidae, family Tethyidae
--2 has members: sea hare, Aplysia punctata - Aplysia, genus Aplysia, Tethys, genus Tethus - type genus of the family Aplysiidae