Phylum Platyhelmithes - Phylum Platyhelmithes (ch. 14)...

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Phylum Platyhelmithes (ch. 14) General Characteristics – 20000 species Bilateral symmetry o Cephilization Some free living; most parasitic o 80% are parasites Triploblastic Acoelomate o Solid body; only cavity is digestive tube Gastrovascular cavity o With the sac body plan, there is only one opening to the gut Branched intestines o o Exception: cestoda (diffusion) “excretory” structures o Osmoregulation o Protonephrida with flame cells o Excretion largely by diffusion Nervous system and cephalization o “brain” composed of ganglia o 1-5 pairs of longitudinal nerve cords o Nerves connect the two cords (ladder)
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o Sense organs Ocelli (eye spots) Auricles (chemosensory) Sexual and asexual reproduction o Monecious o Internal fertilization No respiratory system o Diffusion No circulatory system o Diffusion TAXONOMY Class turbellaria Free-living flatworms; mostly marine
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Phylum Platyhelmithes - Phylum Platyhelmithes (ch. 14)...

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