cnidaria

• PHYLUM CNIDARIA PHYLUM CNIDARIA from Greek knide ‘nettle’ or stinging cells
• Radial symmetry or biradial symmetry.
• Diploblastic tissue-level organization.
• Two types of individuals: polyps and medusae
• Gelatinous mesoglea between the epidermal and gastrodermal tissue layers. It functions as hydrostatic skeleton (for support and flexibility)
• Gastrovascular cavity (an incomplete gut, which has only one opening that serves as both mouth and anus)
• . Specialized cells, called cnidocytes, used in defense, feeding, and attachment. Cnidocytes house stinging organelles called nematocysts. It helps to paralyze their preys by injecting venom. Cnidocil triggers the nematocyst
• Asexual reproduction by budding in polyps forms clones and colonies; Sexual reproduction by gametes in all medusae and some polyps; monoecious or dioecious
• No excretory or respiratory system

  No coelomic cavity
• Class Anthozoa

  Cnidocytes lack cnidocil

  Absent Rhopalium or Velum*

  Ex Sea Anemones and Corals
• Class Scyphozoa

  Cnidocytes present

  medusa is dominant.

  Rhopalium is present

  Moon Jelly

  
• Class Cubozoa

  Contains dangerous nematocysts

  Cuboidal Medusa

  Rhopalium is presen

  Australian Box Jellyfish