Flatworms and Roundworms Chapter 12.3 Flatworms and Roundworms

Flatworms A worms is an invertebrate with soft bodies and bilateral symmetry. They also have 3 tissue layers, with organs and organ systems. Flatworms have flattened bodies. Members of this group are planarians, flukes, and tapeworms. Most are parasites – they feed on other organisms. A free-living organism doesn’t depend on another organism for food or a place to live.

Planarians Planarians are free-living. They have 2 eyespots (can detect light and dark). They have 1 body opening and a tube called a pharynx that connects the mouth and digestive tract. A planarian eat small organisms and dead bodies of larger organisms. They live in freshwater. Planarians reproduce asexually by regeneration. If a planarian gets cut in half each half will form a new planarian. Most are also hermaphrodites.

Flukes Flukes are parasites with a complex life cycle. Most reproduce sexually. One of the diseases caused by flukes is schistosomiasis – these flukes live in the blood.

Tapeworms The adult tapeworm has hooks an suckers to attach to the intestine of the host. Dogs, cats, and humans are hosts for tapeworms. The tapeworm does not have a mouth or digestive system instead it absorbs food that the host digests. A tapeworms grows by making new body segments and they can be very long. These segments will break off and this is how the tapeworms reproduces.

Roundworms Many roundworms are parasites. They can also be called nematodes. They are found in soil, animals, plants, freshwater, and salt water. Roundworms are slender and tapered at both ends. There are male and female roundworms, and reproduce sexually. Nematodes have 2 body openings – a mouth and anus. The anus is the opening at the end of the digestive tract where wastes leave the body.

Importance of Roundworms Some roundworms cause disease in humans. Nematodes can cause damage to many plants. Some roundworms feed on termites, fleas, ants, beetles, and other insects that can be pests. Roundworms also provide nutrients to the soil.