Applied to corals that contain zooxanthellae and are reef forming. Modern scleractinian hermatypic corals are characterized by the presence of vast numbers of symbiotic zooxanthellae (unicellular dinoflagellates) in their endodermal tissue. They live in waters of normal marine salinity, at depths of up to 90 m, in temperatures above 18 °C, and grow vigorously in strong sunlight.