Eutropical subsea

A Eutropical subsea is a low-latitude, circumequatorial body of water within a eutropical, that is genuinely tropical rather than sub-tropical ecozone. It is applied to marine waters considered truly tropical, in which the temperature does not drop below 20 degrees Celsius (68 Fahrenheit). Generally the fauna are derived from Tethys Ocean lineages of the Eocene.
Eutropical subseas are distinguished from paratropical subseas by the presence of coral and accompanying carbonate beds in the form of lagoons. Seagrass is present with mangrove forests supporting mollusks of horned snails, Conch, sea snails of the families "Xenophoridae", and "Turbinellidae". The taxa are usually geographically bound and cannot exist at higher or lower, that is equatorial latitudes.
References.
Primary source: Petuch, Edward J., Cenozoic seas: the view from eastern North America, .