3454chapter14 - Chapter 14 Platyhelminthes Phylum -fat...

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Unformatted text preview: Chapter 14: Platyhelminthes Phylum Platyhelminthesplaty-fat, helmins-worm Flatworms, fukes and tape worms Free-living or parasitic 15,000+ species in our classes Acoelomate with primary bilateral symmetry Bilateral symmetry useul or motile, directional animals Ventral/dorsal, anterior/posterior, right/left Mesodermal parenchyma cells and Fbers packing space between ecto- and endoderm (Nemertea and Gnathostomulida also acoelomate, bilateral) Triploblasticthree true tissue layers, with mesoderm derived from endoderm Organ level of development Very at (thus name) to allow gas exchange by diffusion (no circulatory system) Structure and unction Nutrition and Digestion Carnivorous or parasitic Sac-like g-v cavity with single mouth opening in all classes except Cestoda (no gut) Excretion and Osmoregulation Protonephridiaextensive tubes throughout the animal that absorb nitrogenous wastes Flame cellsfagellated cells at openings that pump fuid through ducts Wastes are released through a terminal pore or pores Nervous system and sense organs Range in complexity from a nerve-net pattern to cerebral ganglia and paired nerve cords Cephalization is obvious with ocelli (light sensitive spots) at anterior end in turbellarians Tactile and chemosensory cells are abundant and may be concentrated at the anterior Auriclesear-like lobes in turbellarians with chemosensory function...
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This note was uploaded on 11/29/2009 for the course BIOL 3454 taught by Professor Lab during the Spring '08 term at UT Arlington.

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3454chapter14 - Chapter 14 Platyhelminthes Phylum -fat...

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