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This 4 page Class Notes was uploaded by Beatrice Deckow I on Monday September 28, 2015. The Class Notes belongs to BIOL 303 at George Mason University taught by Staff in Fall. Since its upload, it has received 7 views. For similar materials see /class/215109/biol-303-george-mason-university in Biology at George Mason University.
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Date Created: 09/28/15
Worms Platyhelminthes Nematoda Annelida numerous animal phyla are worms of one kind or another We are only looking at three phyla of worms also we are NOT going in taxonomic order in what follows Usually many more groups are covered before getting to the Annelids or Nematodes your book turns everything upside down here Phylum Platyhelminthes Flat worms 12000 species Fig 3310 p 675 Bilateral symmetry this is often a result of moving in one direction thus having a head end attened dorsoventrally thin from front to back anatomical terms learn them see the start of the pig dissection in the lab manual for more terms have mesoderm and are generally much more complicated than cnidarians but still fairly primitive for animals all higher animals have three layers gut if present only has a single opening acoelomate no body cavity have distinct organs and organ systems e g digestive nervous reproductive etc but NO circulatory system Classes you need to know TABLE 332 p 674 Turbellaria Planarians and similar similar to Fig 339 p 675 mostly marine and free living Carnivorous have a simple excretory system to remove nitrogenous wastes ame cells more later in the semester finely divided gastrovascular cavity brings food to all parts and allows for better digestion move by using several different muscle groups working against a hydrostatic skeleton or by using cilia hence turbellaria simple brain eyespots Even show some learning ability reproduce asexually through regeneration or sexually hermaphroditic Monogenea ukes mostly ectoparasites of sh Trematoda ukes Fig not in book are parasitic live in organs and tissues of their host many cause important diseases of humans some general characteristics two suckers have at least two hosts will explain this shortly adults reproduce sexually and have a high reproductive potential why juveniles can reproduce asexually Example schistosomiasis or sometimes billharziaOVERHEAD fig 3311 p 675 fertilized eggs exit host through feces eggs develop into ciliated larvae which then infect snails Once inside the snail they reproduce asexually and develop into larval ukes which are then released these larval ukes bore through skin of humans move to veins that bring blood from small intestine to liver and feed off of host reproduce sexually producing many eggs These are released into feces or in some species urine Schistosomiasis is very debilitating body pains dysentery anemia lack of energy has also been linked to increased rates of some cancers and is a major medical problem in many parts of Africa and South America Don t go swimming or wading in stagnant fresh water areas An estimated 207 million people are infected An example Aswan dam disease incidencejumped from 5 to 75 This is progress Can be cured though as usual cure is easier to get in wealthy countries Cestoda tape worms also parasitic in many di erent groups head or scoleX anchors worm to intestine following scoleX are proglottids which are segments that are mostly sacs of reproductive tissues As these develop eggs form inside them Toward end of worm proglottids are mature and burst open to release eggs into feces no digestive system why cause nutritional de ciencies since a lot of food feeds the worm instead of the person diet Phylum Nematoda round worms 90000 described species though probably many more exist Fig 3325 p 683 round mostly circular in cross section pseudocoelom a body cavity not located within mesoderm though it functions much the same do not have cilia but have a thick cuticle Together with pseudocoelom which provides a hydrostatic skeleton provides a skeleton for the worm complete digestive tract mouth gt anus only have longitudinal muscles Therefore move by thrashing or whipping around bend from one side to the other no circulatory system probably the most numerous group of animals in terms of numbers of individuals 90000 found in one rotten apple many important pests and parasites in this group Some examples Filarial worms one species can clog lymphatic vessels leading to elephantiasis Spread by mosquitos Was on the decrease but recently increasing again Trichinella go over life cycle raw undercooked meat eaten often pork in this country though claims are made that this has gotten much better larvae break out of cyst mature to adults in gut adults mate females embed in walls of intestine larvae released into blood or lymph larvae migrate to skeletal muscles and encyst problem feeding pork to pork Ascaris hookworm Guinea worm etc Finally pinworm affects 60 of kids in the United States Fortunately not a serious parasite But many most species are free living eg vinegar eels used in lab Phylum Annelida segmented worms about 12000 species an old theory says they gave rise to the arthropods More recent information seems to contradict this though earthworms and leeches probably best known examples Major characteristics Fig 3322 p681 true coelom though partitioned by septa segmented septa are incomplete in polychaetes digestive tract blood vessels nerve cords run the length of the animal heart actually pumping blood vessels and blood vessels present earthworms respire through skin closed system metanephridia a primitive kidney brainlike ganglia hermaphroditic but cross fertilize clitellum is reproductive organ muscles circular longitudinal others