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Flatworms Planarians, Flukes, tapeworms and Nematodes Platyhelminthes: Flatworms Dorso-ventrally flattened Three tissue layers Some degree of CEPHALIZATION…Lucas! Sac like body plan. Is this good or bad? What might be a better option, why? Goal for the day Discuss three distinct classes of phylum Platyhelminthes. Turbellaria: Planarians Trematoda: Flukes Cestoda: Tapeworms Platyhelminthes is a phylum of the kingdom Animalia. There are approximately 20,000 different species, of which the majority are parasitic. They live in marine, freshwater, and damp terrestrial environments. Platyhelminthes can be divided into four classes: Phylum Pheatures Platyhelminthes are characterized as having very thin bodies between the dorsal (back) and ventral (stomach) surfaces. They range in size from practically microscopic to over 20 meters long. Platyhelminthes have a spongy body structure because they are acoelomates and only possess a mouth. They also lack a complete digestive system. Flat worms exhibit bilateral symmetry, have no internal cavity, have Protonephridial excretory organs rather than an anus, and have a nervous system of longitudinal fibers. Flatworms do not have skeletons; however they do have an endoderm, mesoderm, and ectoderm as well as a head region Overview Locomotion: have a hydrostatic skeleton, (body compartment filled with fluid). They move mainly by contracting muscles against the hydrostatic skeleton. Flatworms have and two layers of muscles under their skin, which assist with movement. Respiration: lack respiratory organs, absorb oxygen through their skin by diffusion. Respiration occurs throughout the length of the body of a flatworm. Metabolic Waste: simple excretory system. Ammonia is excreted directly through their skin by diffusion. Excretory cell: "flame cell". Flame cells are hollow and have tufts of cilia; when the cilia move, they resemble flames and force out waste products. Circulation: They are acoelomates, meaning they lack body cavities and circulatory organs. Circulation, like respiration, occurs through diffusion. Reproduction: their reproductive systems are among the most complex in the animal kingdom. hermaphroditic. One or two ovaries and numerous testes are usually present in flatworms. Flatworms lay eggs that either hatch into tiny worms or a larval stage with cilia. Class Turbellaria: Planaria Free living and aquatic (not parasitic) Found in damp soils, mud, slow moving streams Digestion and Movement Have Pharynx: muscular tube that acts like a mouth Conducts food into gastrovascular cavity (intestine). GVC: extends both to the anterior and posterior to conduct nutrient throughout. (no circulatory system) Relies on diffusion and the body movement. Relies on CILIATED GLIDING for movement Cilia are found on ectodermal cells. Can also twist and tern with muscles which ‘push’ against the MESODERM Planaria Get your Ganglion on. Posses eyes spots like our old friend clammy danny. Only light detectors, not actual eyes These multicellular eyespots are a specialized mass of nerve cells called a GANGLION. Because its located at the ANTERIOR region, and they’re specialized, sometimes called a primitive brain. And yeah, we’re talkin’ bout cephalization finally. Not a ganglion…its a gang of lions No comment…but also not a ganglion. Other features Other features make these creatures significantly more complex than Cnidarians: Cephalization Pair of nerves with cross branches from the eye spots called LADDER-LIKE Nervous system Flame Cells Found at the end of tubes called nephridiophores. Cilia beat collecting waste fluid into tubes which then end in a pore to the outside of the organism through nephridiopores. Reproduction Hermaphrodites: ‘shed’ their sperm into the water surrounding them through their ventral surface. Sperm are taken into a genital pore where ova are fertilized Embryos become larvae before turning into adults. Flukes & Tapeworms Trematoda and Cestoda Flat, and similar to Planaria. Parasitic http://animal.discovery. com/videos/monstersinside-me-meter-longtapeworm.html Parasitism Results in two characteristics. How do you think a tapeworm or parasites needs and development would different? 1. Diminished need for specializations in: Digestion and obtaining food, and responding to the world. 2. Increased need for specialization for offspring survival, transferring them to another host is ideal. Parasites rarely kill their hosts, why? Results in multi-host, polymorphic lifestyle Parasites continued Tapeworms are also unique because: Lack cephalization. No true head Do have a SCOLEX: specialized hooks and suckers for attachment to mammalian intestines PROGLOTTIDS or reproductive packages extend from the scolex and have male and female sex organs. Cross fertilization happens between tapeworms when possible. Scolex continuously produces immature proglottids, which get nutrients from their environment until developed. Lifecycle Nematodes Nematodes: Roundworms Nematodes, also called roundworms, are the most abundant multicellular animals on Earth. There are more than 15,000 identified species of nematodes, and scientists are still discovering new ones! Most nematodes are 1-5 millimeters (mm) long, but scientists have identified a few very long nematodes, too, like Placentonema gigantisma, an 8-meter-long nematode found in the placenta of a sperm whale. All nematodes have fairly simple body plans. These animals are tube-like in shape; have an outer body wall, called a cuticle; and a digestive track that runs most of the body length. Because of this relatively simple body plan, nematodes are sometimes described as "a tube inside a tube.” Decomposition Free-living nematodes are very important and beneficial in the decomposition of organic material and the recycling of nutrients in soil. Nematode bacterivores and fungivores do not feed directly on soil organic matter, but on the bacteria and fungi which decompose organic matter. The presence and feeding of these nematodes accelerate the decomposition process. Their feeding recycles minerals and other nutrients from bacteria, fungi, and other substrates and returns them to the soil where they are accessible to plant roots. Despite a simple body plan, nematodes are complex animals. Scientific research using a variety of nematodes has been important in understanding ecology, medicine, and basic biology. One of the most well-studied nematodes is Caenorhabditis elegans. C. elegans are approximately 1 mm long, are found in soils all over the world, and feed on bacteria. Where can you find nematodes? Just about everywhere. They're residents of many different habitats, including soil, plants, freshwater, and saltwater. Some nematodes are even parasitic, meaning they live, grow, and reproduce inside other organisms at the expense of their host's health. Such a wide range of habitats also means that among the various nematode species, there is a lot of diversity in what they eat. Soil nematodes include bacterivores (bacteria eaters), fungivores (fungus eaters), algivores (algae eaters), and herbivores (plant eaters). Roundworms No longer ventrally-dorsally flattened Have a tube-like intestine Made possible by new body cavity called a PSDUEDOCOELOM. (*see-lum) Also allows for longitudinal muscles. Side to side moves. Flatworms are acoelomates, meaning they have NO body cavity a coelom was a significant advance in animal body structure because it repositions fluid and allows complex tissues and organs to develop Body plans. Final notes Circulation is through diffusion: no circulatory system No skeletal system: Most excretion is through diffusion But complex reproductive lifecycles. Where do they fit in a food web? http://www.youtube.com/watch?v=wGj7QOP9hjk&fea ture=related Worms are responsible for everything!