Cnidarians are carnivores that use tentacles arranged in a ring around the mouth to capture prey and push the food into the gastrovascular cavity, where digestion begins. The undigested remains are egested through the mouth/anus. The tentacles are armed with batteries of cnidocytes, unique cells that function in defense and the capture of prey (FIGURE 29.9) Cnidocytes, which contain stinging capsules called nematocysts, give the phylum Cnidaria its name (Gr. Cnide,”nettle”).