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2010-07-25 00:50:17
Parazoa Porifera Invertabrates

The Parazoa Group
Show Answers:

  1. What is the defining feature of the Parazoa group?
    A lack of true tissues
  2. Which Phylum is included in the Parazoa group?
  3. Which organism is the Porifera believed to have evolved from?
    Unicellular Choanoflagellates - Tiny, single-celled protists with a characteristic collar and flagellum that usually live in colonies. Some sponge cells are almost identical to choanoflagellates.
  4. How many species of Porifera are there?
    About 15000
  5. When did Porifera evolve?
    In the Precambrian era - around 700 mya
  6. Describe the structure and function of an ostia in a Porifera.
    A hole in the body wall of the sponge made from a porocyte. It allows water flow into the spongoceal from the outside environment and filters food out.
  7. Describe the Pinacoderm. (Porifera)
    The outer layer of cells that is contacting the environment and consists of a single layer of pinacocytes that may be modified to form porocytes.
  8. Describe the Mesohyl. (Porifera)
    Gelatineous matrix between inner and outer layers that contains Amoebacytes.
  9. List the functions and transport of Amoebacytes in Porifera.
    Nutrient transport, gamete formation, secrete the skeleton.
  10. List the different types of skeleton possible in Porifera.
    Spongin (collagen-like protein) Spicules (made from calcium carbonate or silica) or spicules embedded in spongin.
  11. Describe the Choanoderm in Porifera.
    Inner layer that lines the spongocoel and consists of a single layer of choanocytes
  12. List the functions of Choanocytes in Porifera.
    In some species they form gametes, but their main function is feeding.
  13. Describe the structure of a Choanocyte in Porifera.
    They have a flagellum which beats to create the flow of water and a mucous-coated collar which traps food particles.
  14. How is food processed from the outside environment to the cells of the body wall in Porifera?
    The Choanocyte's collar traps food which is taken up into vaculoes and digested using enzymes. It is then passed onto amoebacytes which distribute nutrients to other cells in the mesohyl and pinacoderm.
  15. What are the three classes of Porifera?
    Calcarea (400 spp. calcium carbonate spicules, tend to be small and tubular or vase-shaped) Demospongiae (95% of spp, very diverse, spongin and silicaceous spicules, include "bath sponges") and Hexactinellida (nearly all deep-sea spp, mostly vase- and funnel-shaped ranging from 7.5cm-1.3m)