Porifera Quiz

Phylum Cnidaria 11,000+ Species

Cnidarian examples include    

     -Sea Anemones

    -Sea Jellies

    -Coral

Cnidarian Characteristics

    -Radial symmetry or Biradial

    -Diploblastic Tissue level (have only 2 layers)

         -They have a gelatinous Mesoglea

    -Gastrovascular Cavity (this cavity works as their stomach)

         -Nerve Net (no brain. The nerve net just responds to stimuli like a reflex)

    -Cnidocytes (These are the stinging cells)

          What makes Cnidarians stand out is their cnidocytes

              -Cnidocytes are stinging cells located on tentacles

             -Cnidocytes discharge a harpoon like stinging structure called a nematocyst

Cnidarians have two body structures

    -Polyp

          -The polyp form is sessile. It attaches to a rock or other surface and tentacles grow upwards. The sea anemone is a polyp form.

    -Medusa

          -The medusa is a free swimming form. It has a bell on top with tentacles hanging downward. A sea jelly is a medusa form. 

Cnidarian Classes

    Hydrozoa

        -Hydras

        Characteristics:

                -Cnidocytes present in the epidermis; gametes produced epidermally and always released to the outside of the body; mesoglea is largely ascellular; medusae usually with a velum; many polyps colonial; mostyl marine with some freshwater species

    Scyphozoa

        -Common Sea Jellies

        Characteristics:

                -Medusa prominent in the life history; polyp small; gametes gastrodermal in origin; and released into the gastrovascular cavity; cnidocytes present in the gastrodermis as well as epidermis; medusa lacks a velum; medoglea with wandering mesenchyme cells; all are marine

    Staurozoa

        -polyps

        Characteristics:

            -Medusae absent; develop from benthic planula larvae; eight tentacles surrounding the mouth; attachment to substrate by adhesive disk; sexual reproduction only; all marine

    Cubozoa

        -Cube shaped sea jellies

        Characteristics:

            -Medusa prominent in life history; polyp small; gametes gastrodermal in origin; medusa cuboidal in shape with with tentacles that hang from edges of the bell; all marine

    Anthozoa

        -Anemones and corals

        Characteristics:

            -Colonial or solitary polyps; medusae absent; cnidocytes present in the gastrodermis; cnidocils absent gamets gastrodermal in origin; gastrovascular cavity divided by mesenteries that bear nematocysts; internal biradial or bilateral symmetry present; mesoglea with wandering mesenchyme cells; tentacles solid; All marine

Sea jellies have a strange life cycle. They go through a complex alternation of generations