Most cnidarians are carnivorous and their diet consists mainly of small crustaceans. They capture prey in a rather passive manner—as it drifts through their tentacles the cnidarian discharge stinging nematocysts that paralyze the prey. They use their tentacles to draw the food into their mouth and gastrovascular cavity. Once in the gastrovascular cavity, enzymes secreted from the gastrodermis break down the food. Small hair-like flagella that line the gastrodermis beat, mixing enzymes and food until the meal has been fully digested. Any no-digestable material that remains is ejected through the mouth with a swift contraction of the body.
Gas exchange takes place directly across the surface of their body and waste is released either through their gastrovascular cavity or by diffusion through their skin.
