Which is not a zone in the three-layered structure of the ocean relating to density?

Not sure if you have any answer choices to pick. however i'd say its the intertidal zone

The  pelagic  region is divided into three zones. the top zone is the euphotic or sunlit zone. this is the ocean zone that sunlight penetrates. because this zone gets sunlight, photosynthesis can occur and plants can grow here.sub  zones. the oceanic zone is subdivided into the epipelagic,  mesopelagic, and bathypelagic zones. the epipelagic (euphotic) zone, also called the sunlit zone, receives enough sunlight to support photosynthesis.your question does not include multiple choice,but i can give you some info on what the 3 zones hope this : -)