lab 2 - Laboratory 2 Animal Diversity II I Germ Layers A...

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Laboratory 2 – Animal Diversity II I. Germ Layers A. Ectoderm 1. outer germ layer; gives rise to stem & nervous system B. Mesoderm 1. middle germ layer; gives rise to connective tissue, muscle, bone, blood vessels, kidneys, & other structures C. Endoderm 1. inner germ layer; gives rise to lining of respiratory & digestive tracts II. Body Cavity - space between gut tube (lined with endoderm) & body wall (with its outer covering of ectoderm) A. Acoelomate 1. body plan in which there is no body cavity 2. ex, flatworm (liver fluke) B. Pseudocoelomate 1. Body plan in which body cavity is lined by mesoderm on one side & by ectoderm on the other 2. ex. Phylum Rotifera & Nematoda C. Coelomate 1. body plan in which body cavity is completely lined with mesoderm 2. ex. vertebrates III. Blastospore A. Opening into body cavity of an early embryo that eventually becomes either the mouth (in protostomes) or the anus (in deuterostomes) of the organism IV. Organisms & Evolutionary Trends A. True tissues & 3 distinct germ layers B. Body cavity (pseudocoelom or true coelom) C. Digestive tract & 1 way digestive system D. Circulatory system & closed system E. Cephalization = anterior concentration of sensory organs V. Adaptations for Parasitism A. Adhesive structures (suckers & hooks) 1. facilitate attachment to a host B. Sensory organs 1. important in free-living organisms that must negotiate complex environments 2. reduced in many parasites that spend much of life cycle attached to host C. Feeding modifications 1. reduction of digestive tract & direct absorption of food through body wall in endoparasites that can rely on host to perform digestive functions D. Increased reproductive capabilities (proglottids) 1. necessitated by low probability with which a multiple-host life cycle can successfully be completed E. Either asexual reproduction or hermaphroditism 1. often employed due to low probability of encountering mate when attached to host
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VI. Acoelomates A. Phylum Platyhelminthes 1. many members of group are dorsoventrally (from top to bottom) flattened 2. bilaterally symmetrical, with 3 germ layers 3. lack body cavity or coelom 4. have advanced nervous, digestive, muscular, excretory, & reproductive systems 5. lack specialized organs for gas exchange & circulation 6. Class Turbellaria a. Planarians, group of free-living freshwater flatworms b. pharynx (on ventral surface) can protrude & retract c. eyespots help organism distinguish light from dark d. region of parenchymal cells of mesodermal origin between ectoderm & endoderm 7. Class Cestoda a. ex. tapeworms Eyespot Auricle Testes Gastrovascular Cavity Pharyngeal Pouch Pharynx Mouth Ciliated epidermis epidermis Gastrovascular cavity Pharyngeal cavity Pharynx Gastrovascular cavity Proglottids Budding zone (immature proglottids) Scolex Neck Suckers Rostellum with hooks
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b. head (scolex) has suckers & several rows of hooks c. highly adapted to parasitic lifestyle i. most organ systems are degenerate, while reproductive system is highly developed d. proglottids i. segments posterior to scolex that contain male & female reproductive organs ii. fertilization may take place within each proglottid
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