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Learning Intentions

Learning Intentions. By the end of this lesson, you will be able to: Identify general characteristics of Phylum Cnidaria Describe functions of major structures in terms of life functions and explain their evolutionary significance (adaptations) Recall key ecological roles of cnidarians.

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Learning Intentions

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  1. Learning Intentions By the end of this lesson, you will be able to: • Identify general characteristics of Phylum Cnidaria • Describe functions of major structures in terms of life functions and explain their evolutionary significance (adaptations) • Recall key ecological roles of cnidarians

  2. Phylum Cnidaria

  3. General Characteristics • Two life forms (polymorphism): swimming medusae and sessile polyps • All cnidarians have cells called cnidocyteswhich contain poisonous threads called nematocysts. • Bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium (ectoderm) that are mostly one cell thick. • Radial symmetry with mouths surrounded by tentacles that bear cnidocytes.

  4. Structure Cont’d…

  5. Structure Endoderm Ectoderm

  6. Structure Cont’d…

  7. Feeding • Capture organisms by using nematocysts • Tentacles push food into mouth • Endoderm develops into gastrodermis (the cells that line the interior digestive cavity and secrete enzymes to digest food extracellularly) • Final digestion happens intracellularly (within cells located in mesoglea)

  8. Gas Exchange/Excretion • Diffusion of gases from water into epithelial cells • Diffusion of wastes from mesoglea into water (pushed out through mouth)

  9. Nervous System • Nerve net: interconnected nerve cells spread out through mesoglea • Allows for coordination of muscles and tentacles, firing of nematocysts

  10. Circulation • None: Diffusion

  11. Reproduction

  12. Ecological Roles • Corals provide diverse habitat for other organisms • Food for other organisms (turtles, fish) • Active predators • Protection – sea anemones & clown fish

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