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Flatworms. Roberto Nunez Andy Navarrete. What is a Flatworm?. Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have 3 embryonic germ layers, bilateral symmetry, and cephalization . Part of the phylum platyhelminthes
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Flatworms Roberto Nunez Andy Navarrete
What is a Flatworm? • Flatworms are soft, flattened worms that have tissues and internal organ systems. • They are the simplest animals to have 3 embryonic germ layers, bilateral symmetry, and cephalization. • Part of the phylum platyhelminthes • Flatworms are known as acoelomates, meaning “without coelom”(a coelom is a fluid-filled body cavity that is lined with mesoderm).
Continued… • No Coelom forms between the tissues of flatworms. • Flatworms also have bilateral symmetry which means that the animal has 2 well-formed sides that can be identified as left and right. • Most flatworms exhibit enough cephalization to what have what is called a head.
Food Consumption • Free living flatworms can be carnivores that feed on tiny aquatic animals, or they can be scavengers that feed on recently dead animals. • They can also be scavengers. • Flatworms have a gastrocavascular cavity with a mouth where food and wastes pass. • The flatworms use the pharynx(a muscular tube) to pump food into the cavity where after it is digested by the cells of the gut.
Parasitic Flatworms • They feed on blood, tissue fluids, or pieces of cells within the host’s body. • Many of these worms obtain nutrients from foods that have already been digested by the host. • That leads to having a simple or no digestive system for these worms.
Respiration, Circulation, and Excretion • Flatworms do not need a circulatory system because of their flat and thin bodies. • Instead, they rely on diffusion to transport oxygen and nutrients to their internal tissues, and to remove carbon dioxide and other wastes from their body. • They have no respiratory organs. • Flatworms have flame cells(specialized cells that filter and remove excess water from the body) to function in excretion.
Responding To Their Environments • A head encloses several ganglia(groups of nervous cells) that control the nervous system. • The parasitic flatworms interact little with the environment and usually have a simple nervous system • Free-living flatworms usually have an eyespot on the anterior end of their body.
Moving • Free-living flatworms have 2 ways of moving: • Cilia on their epidermal cells that help them glide through water. • Muscle cells which let them twist or turn in reaction to their environment.
Reproduction For Flatworms • Most free-living flatworms are hermaphrodites(has both male and female parts) that reproduce sexually. • During this, 2 worms join in a pair and deliver sperm to each other. The worms are laid and hatch within a few weeks.
Turbellarians • Are free living flatworms that live in marine or fresh water. • Most live in the sand or mud under stones and shells. • The most familiar are the “cross-eyed” freshwater worms.
Flukes • Are parasitic flatworms that can infect any of the internal organs of their host. • Its primary host is somewhere that it reproduces sexually. • An intermediate host is an organism in which a parasite reproduces asexually. • For the blood fluke Schistosomamansoni, a human would be its primary host, and a snail would be its intermediate host.
Tapeworms • Are long, flat, parasitic worms that are adapted to life inside the intestines of their hosts. • Have no digestive tract • Attaches to the host using hooks or suckers on its scolex. • Have proglottids on each end the break off and release eggs that are then fertilized and carried throughout the host.
