Cnidaria Cnidarians include hydroids, sea anemones, corals and jellies. This group is more advanced than the sponges, and has a tissue level of construction. Basic anemone structure.
Cnidarians have a true mouth and digestive cavity, but no anus.
Tentacles surround the mouth opening to trap prey. These animals are usually carnivores, eating crustaceans, molluscs and small fish. The zooxanthellae provide oxygen and some nutrition and are important for coral reef formation. Basic jellyfish structure. Cnidarians are made unique by the present of stinging organs called nematocysts.