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Platyhelminthes

Platyhelminthes. Figure 33.10 Anatomy of a planarian. Characteristics of platyhelminthes. Simplest animals that are bilaterally symmetrical – flat body with head (senses) and hooks or suckers triploblastic (composed of three fundamental cell layers) Ectoderm Endoderm Mesoderm - muscles

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Platyhelminthes

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  1. Platyhelminthes

  2. Figure 33.10 Anatomy of a planarian

  3. Characteristics of platyhelminthes • Simplest animals that are bilaterally symmetrical – flat body with head (senses) and hooks or suckers • triploblastic (composed of three fundamental cell layers) • Ectoderm • Endoderm • Mesoderm - muscles • Have no body cavity other than the gastrovascular cavity, and lack an anus – two way digestive tract. • Primitive Nervous System • Ganglion-collection of nerve cell bodies

  4. Classes(Parasitic tapeworms and flukes) • Modified body plan with resistent body cuticle and head hooks and suckers(scolex) • Tapeworm:proglottid-reproductive body segments

  5. Figure 33.12 Anatomy of a tapeworm

  6. Figure 33.11 The life history of a blood fluke, Schistosoma mansoni

  7. Physiology of Planaria • Locomotion –mesodermal muscles; ciliated ventral cells with mucus • Food-Getting- ventral mouth via pharynx(a muscular extendable tube) ; into gastrovascular cavity • Digestion- 2-way digestive system (one opening); branched gastrovascular system; extracellular digestion by enzymes followed by intracellular completion • Excretion- liquid excretion across body surface; some fluid balance by protonephridia and “flame cells; solid waste via mouth

  8. Physiology of Planaria • Circulation- gastrovascular cavity and cyclosis in cells • Respiration- gaseous exchange across cell membranes and body surface • Nervous system- brain ganglia with longitudinal nerve cords; sense organs: chemical, mechanical and light (via pigmented eyespots) sensitive • Reproduction- asexual: regeneration sexual: hermaphroditic- exchange sperm- fertilization internal and eggs laid in jelly or cocoons

  9. Aschelminthes - Roundworms

  10. A. Characteristics • Three germ layers • Bilateral symmetry – tube within a tube body plan • One-way digestive tract – mouth and anus openings (specialization) • Free living and parasitic • Found in soil, fresh and salt water • Pseudocoelom – cavity NOT completely surrounded by mesoderm

  11. B. Representative Examples • Ascaris – roundworm found in many animals, adults develop in digestive tract, lay eggs that may be injested by another host and develop in new host • Trichinella – adult in intestine, larva migrate to muscles and encyst, others eat uncooked meat and larva develop • Heartworm – dog and mosquito • Hookworms – larva penetrate feet

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