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Platyhelminthes The Flatworms
Pechenik: 34,000 spp (Brusca & Brusca: 20,000 spp) Characteristics: Triploblastic Ectoderm, mesoderm, endoderm Acoelomate Bilateral symmetry (w some cephalization) Protonephridia = Organs for excretion/osmoregulation Flatness allows diffusion for gas exchange 80% are parasitic Simultaneous hermaphrodites (monoecious)
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Phylum Platyhelminthes
Opisthaptor Ectoparasite One host Trematoda Acetabulum endoparasite Mollusc/vertebrate life cycle Cestoda Monogenea Turbellaria Free living Microtriches Scolex Proglottids Cilia lost from ectoderm (parasitic lifestyle) Phylum Platyhelminthes
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Class Turbellaria
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Class Turbellaria
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Class Turbellaria
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Class Turbellaria
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Class Turbellaria
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Class Turbellaria Most are free living Marine & FW Sensory receptors
Chemical (auricles) Tactile Light Dugesia sp.
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Class Turbellaria Most are free living Marine & FW Sensory receptors
Chemical Tactile Light Cephalized Crawl on substrate using cilia Dugesia sp.
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Class Turbellaria Incomplete digestive tract Pharynx
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Class Monogenea haptor opisthaptor
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Class Monogenea Ectoparasites of fish skin and gills Only 1 host
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Monogenea Reproduction: Eggs → oncomiracidium larva → attach to fish
Larva similar to cestode oncosphere Adults resemble digene trematoda (convergent evolution – life cycles very different)
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