Feeding

The feeding habits of unsegmented worms vary depending on their classification as: free-living(planarians) or parasitic(flukes and tapeworms)

Flatworms
Free-living flatworms are variety eaters. They may be carnivores, feeding on tiny aquatic animals, or scavengers, feed on recently dead animals. Their main source for food is the water. They feed on sessile invertebrates, and can vary from, sea squirts, bryozoans, small worms, crustaceans. Some are even cannibalistic. They have a gastrovascular cavity with one opening at the end of a muscular tube called a pharynx(sucks food into the cavity) The enzymes in its intestines breaks down the food and the undigested material is expelled throat the mouth. Food enters and leaves the body of the worm through the mouth.

Parasitic flatworms thrive off of a host species, feeding on blood, tissue fluids, or pieces of cells. They depend entirely on their hosts to digest their food for them. Without a host, there would be no food, thus these organisms would die or go dormant.

Flukes generally alternate between different hosts during their life cycle. It has a mouth at its anterior end. A thick cuticle and 1/more suckers surround the mouth, which function by attaching to the host's internal body surface. Some species have a pharynx that pumps food into a pair off dead-end intestinal sacs, where it is then digested.
Tapeworms usually have two hosts, the adult worm lives in one kind of animal(main) and the larva lives in another(alternate). They have no digestive tract. Along its anterior side, a tapeworm has a scolex, surrounded by hooks and suckers which attach to the host's digestive system. It has no mouth or intestine, must live in the intestine of its host, where it can absorb molecules of food that the host digested. Main hosts; humans. Alternate hosts; animals( fish, cows, pigs, rabbits, etc.)



Roundworms
free-living roundworms are often carnivores, which catch and eat other small animals. Small algae, fungi, or pieces of decaying organic matter are a favourite of some soil-dwelling and aquatic forms. Others prefer to digest bacteria and fungi which act as decomposers.

Parasitic roundworms include those that live in the soil and attach to the root hairs of green plants. They suck out the plant juices and cause great damage, and are commonly found in tomato plants.