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CH 27 Phylum Cnidaria

Explore the world of Cnidarians, with two tissue layers, radial symmetry, and unique body forms - Medusa and Polyp. Discover the differentiation of cells, stinging cnidocytes, and the intriguing Obelia life cycle. Learn about the groups of Cnidarians like Hydrozoa, Scyphozoa, and Anthozoa, as well as the Phylum Ctenophora featuring Comb Jellies.

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CH 27 Phylum Cnidaria

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  1. CH 27 Phylum Cnidaria Jelly-fish, coral, sea anemones, and hydras

  2. Characteristics of Cnidarians • Cnidarians have two tissue layers and radial symmetry • Epidermis, • Gastrodermis • Mesoglea is the jelly – like substance between the layers. • Cnidarians have two basic body forms • Medusa, free floating and are often umbrella shaped • Polyp, tube - like and attach to a rock or some other object

  3. Visual Concept: Comparing Medusa and Polyp Bodies

  4. Differentiation of Cells • Cnidarians have nerve cells arranged into nerve net • Sensory cells • Muscle - like cells • Stinging cells (cnidocytes)

  5. Stinging Cells: Cnidocytes • Cnidocytes are located on fingerlike tentacles that surround the one opening. • Each cnidocyte has a threadlike organelle called a nematocyst • That can contain toxins • Used for defense and to capture prey

  6. Visual Concept: Cnidocytes

  7. Reproduction • Sexual and asexual reproduction occurs in both forms • In Obelia, the life cycle alternates between a polyp and a medusa stage. • Once the gametes fuse, a planulae forms as a free-swimming larvae.

  8. Obelia Life Cycle

  9. Groups of Cnidarians • The three main groups of cnidarians are; • Class Hydrozoa (Colony, Portuguese man – of – war) • Class Scyphozoa (Common jelly fish) • Class Anthozoa (“flowering” animals, sea anemone)

  10. Phylum Ctenophora: Comb Jellies

  11. Phylum Ctenophora: Comb Jellies • “comb – holder” • 8 comb – like rows of cilia • Move by beating their cilia • Most do not have cnidocytes, instead colloblasts • Secrete sticky substance on two tentacles • Apical organ, direction in water • Hermaphroditic • Bioluminescent

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