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  • KINGDOM ANIMALIAPhylum Cnidaria

  • Phylum Cnidaria

    The phylum name comes from Cnidaria, the Greek word for nettle, a plant that has stinging hairs.

  • Members of the Phylum Cnidaria

    exhibit radial or biradialsymmetry.are all aquatic (typically marine, but some freshwater).are sessile, free-floating, or weak swimming.have a tissue-level organization.have a primitive nervous system.have stinging cells.

  • Question

    Which of the following characteristics sets the members of the phylum Cnidaria apart from all other animals?

    A. They are all aquatic.

    B. They have stinging cells.

    C. They are all multicellular.

    D. They are sessile as adults.

  • General Organization

    Cnidarian bodies are organized around the gastrovascular cavity, where digestion takes place.Two layers of cells: gastrodermis (lining the digestive tract) and epidermis (outer layer)Mesoglea: jelly substance in between the two cell layers.

  • Question

    In a cnidarian, the jelly substance in between the two cell layers is called

    A. mesoglea

    B. cnidoglea

    C. epidermis

    D. gastrodermis

  • Reproduction

    Sexual reproduction: gametes are shed directly into the water.

    Asexual reproduction: usually by budding, some by fission.

  • Question

    Cnidarians reproduce in all of the following ways, EXCEPT

    A. Asexual fission

    B. Asexual budding

    C. Sexual regeneration

    D. Sexual reproduction involving egg and sperm

  • Life Cycles:Polyp and Medusa

    Cnidarians generally alternate between sessile polyps that reproduce asexually and swimming medusae that reproduce sexually.

    One of these stages is missing in many forms.

  • Question

    True or False:

    This picture represents the medusa body plan of a cnidarian.

  • Stinging Tentacles

    The tentacles of all cnidarians produce nematocysts, organelles that can discharge threads to entangle, penetrate, or poison prey.

    The tentacles are composed of cells called cnidocytes, which contain the nematocysts.

  • Cnidocyte

  • Question

    In a cnidarian, the cnidocytesare used forA. swimming

    B. digesting food

    C. paralyzing prey

    D. sensing predators

  • Feeding and Digestion

    Cnidarians prey on a variety of appropriate-sized prey.

    Prey is normally drawn into the gastrovascular cavity by the tentacles.

    Here, gland cells discharge enzymes onto the food.

  • Question

    Where does digestion take place for cnidarians?

    A. In the tentacles

    B. In the epidermis

    C. Outside the body

    D. In the gastrovascular cavity

  • Four Important Cnidarian Classes

    1. Class Hydrozoa

    Mostly marine

    Alteration of generation (polyp and medusa stages) is usually exhibited

    Includes hydroids, fire corals, and Portugese man-of-war

  • Hydrozoan: Hydra

  • Portuguese Man of War

  • Four Important Cnidarian Classes

    2. Class Scyphozoa

    Dominant stage is the medusa

    Polyp is absent or reduced

    Cup-shaped umbrellas

    Includes true jellyfish

  • Scyphozoa: Aurelia labiata

  • Four Important Cnidarian Classes

    3. Class Cubozoa

    Like jellyfishes, but they have cubical umbrellas.

    Some may deliver fatal stings.

    Includes the box jelly, one of the 10 most venomous organisms on earth.

  • Cubozoans

  • Four Important Cnidarian Classes

    4. Class Anthozoa

    Polyps with a flowerlike appearance

    No medusa stage

    All marine, found all over the world

    Includes sea anemones, corals, sea fans, and sea whips.

  • Anthozoans: Corals

  • Anthozoans: Anemones

  • Economic ImportanceReef-building corals provide habitat for fish and other animals that are important as food sources for humans.Coral reefs are tourist attractions and coral rocks are used as building materials and jewelry.