Mostly marine animals with radial symmetry, two germ layers, and stinging cells are called ______, which include jellyfishes, hydras, corals, and sea anemones.

The marine animals described in your question are called Cnidarians. This diverse group is characterized by their radial symmetry, which allows them to be oriented in a circular pattern around a central axis. Cnidarians typically possess two germ layers: the ectoderm and the endoderm, which develop into the outer and inner layers of their bodies, respectively.

A key feature of cnidarians is the presence of specialized cells known as cnidocytes, which contain stinging structures called nematocysts. These cells are used for capturing prey and for defense against predators.

Cnidarians encompass various forms of marine life, including jellyfishes, hydras, corals, and sea anemones. Each of these organisms plays a significant role in marine ecosystems. For example, corals contribute to the formation of coral reefs, which support a vast array of marine species. Overall, cnidarians are essential components of oceanic biodiversity and ecology.