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Phylum Cnidaria

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

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Phylum Cnidaria

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  1. 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) • Class Cubozoa (box jellies, once in Scyphozoa)

  10. Class Hydrozoa • Primary polyp form • Colonial organisms, example Obeila pg 678 • Polyps in colony have specialized “jobs”

  11. Class Scyphozoa • “cup animals” Aurelia • Includes both polyp and medusa forms

  12. Class Anthozoa • “flower animals” • Polyp major form

  13. Class Cubozoa • Box jellies, Sea Wasp Chironex fleckeri • Cube – shaped medusae with 1 – 2 tentacles on each corner • Polyp is inconspicuous • Very small and poisonous

  14. Phylum Ctenophora: Comb Jellies

  15. 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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