Phylum Cnidarian (Coelenterata)
These are typically invertebrate animals, which show a very simple level of tissue organization. They are aquatic animals and are mostly found in marine environments, attached to the rocks at the bottom of the ocean. A few species are also found in freshwater habitats. Coelenterates can be found solitarily or in colonies. You can find them sedentary or free-swimming.
Coelenterates can be called as the simplest animal group that has true tissues and have the characteristic coelenteron of the gastrovascular cavity.