Phylum Platyhelminthes (2009).pdf

Phylum Platyhelminthes (2009).pdf

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BILATERIA Bilateral symmetry - evolution of actively hunting animals Cephalization - concentration of sensory organs in the head region Ectoderm Mesoderm Endoderm Triploblastic - allows development of organ systems Protostomes : blastopore becomes mouth Lophotrochozoa : trochozoa & lophophorates Platyhelminthes ( platy = flat, helminthes = worm) Dorsoventrally flattened 1. Acoelomate 2. Incomplete digestive system (except cestodes) 3. Ladderlike nervous system with simple brain 4. Protonephridial excretory system 5. No vascular system 6. Circular & longitudinal muscles 7. Mostly hermaphroditic 8. Classes of Platyhelminthes Turbellaria Mostly free-living Ciliated epidermis with rhabdites Well-developed sensory structures, e.g., eyespots Monogenea Ectoparasitic flukes Attachment organs (prohaptor & opisthaptor) Direct life cycle; Single host Trematoda Endoparasitic flukes 2 suckers : oral & ventral Complex life cycle; Intermediate & definitive hosts Cestoda Parasitic tapeworms No digestive tract Scolex, neck, strobila made of proglottids
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