Flatworm: Cycloporus venetus
A flatworm has a combination of a digestive and excretory system. It takes food in and gets rid of wastes through the same opening. The blind-ending intestine of trematodes consists of a simple sac with a midventral mouth or a two-branched gut with an anterior mouth. There is normally no anus, but a very few species have one or two anal pores. The pharynx is usually between the mouth and the intestine, along with an esophagus, receiving secretions from glands. The intestine, lined with digestive and absorbing cells, is surrounded by a thin layer of muscles that effect peristalsis. This contract in a wavelike fashion, forcing material down the length of the intestine. In many larger flukes lateral intestinal branches, or diverticula, bring food close to all internal tissues. Undigested residue passes back out of the mouth. Flatworms are carnivorous predators and scavengers. They feed mainly on bacteria, protozoans, other small invertebrates, and other available animal matter.