LESSON 3 PORIFERA AND PLACOZOA

• What are the two phyla that constitute the simplest multicellular animals?

  Phylum Porifera and Phylum Placozoa
• What is the significance of microvillar collars in Porifera?


  They surround flagella and arise from single cells or syncytia.
• How do Porifera feed?


  They are sessile and feed on food particles suspended in water through filter feeding.
• How many described species of Porifera are there?

  8,000 described species
• What percentage of Porifera species are freshwater versus marine?

  2% Freshwater and 98% Marine
• What type of growth do Porifera exhibit?

  Indeterminate growth
• What type of symmetry do Porifera exhibit?

  Amorphous, radial symmetry
• What is alloincompatibility in Porifera?

  It is the ability to distinguish between their own cells and those of different species.
• What happens during isogenic treatments in Porifera?

  Individuals from the same colony always fuse together.
• What occurs during allogenic treatments in Porifera?


  Individuals from different colonies never fuse and show an accelerated response on the second encounter.
• What is the spongocoel in Porifera?

  It is the empty space or cavity of the bag-like body structure.
• What are choanocytes?


  They are cells lining the spongocoel that generate currents and capture food particles.
• What role do archaeocytes play in Porifera?

  They wander through the mesohyl, digest food, store nutrients, and can develop into specialized cells.
• What do sclerocytes secrete?

  Calcareous or siliceous spicules
• What do spongocytes secrete?

  Collagen fibers known as spongin
• What is the function of spicules in Porifera?

  They help maintain shape and discourage predation.
• What are pinacocytes?


  Flattened contractile cells that form a layer called pinacoderm.
• What are ostia in Porifera?

  Narrow openings that perforate the sponge body.
• What is the osculum?


  It is the opening where water exits the sponge.
• What do lophocytes secrete?

  Fine collagen fibers
• How do myocytes function in Porifera?

  They are muscle-like cells that aggregate around the oscula.
• What are the three types of body structure or canal systems in Porifera?

  • Asconoid: Simplest structure; water enters ostium -> spongocoel -> osculum.
  • Syconoid: More complex; increases surface area of choanocyte layer.
  • Leuconoid: Most complex and efficient; spongocoel disappears, forming numerous flagellated chambers.
• What are the methods of asexual reproduction in Porifera?

  • Fragmentation
  • Budding
  • Gemmule formation
• What is the significance of gemmule formation in Porifera?

  Gemmules can survive for up to 25 years and are formed during periods of dormancy.
• How do Porifera reproduce sexually?

  They are hermaphroditic and undergo internal fertilization.
• What happens to developing embryos in Porifera?

  They stay in the mesohyl for a time and are released as swimming larvae.
• What are the types of sponge larvae and their characteristics?

  • Coeloblastula: Flagellated cells directed into the blastocoel; forms amphiblastula.
  • Stereoblastula: Initially hollow, becomes solid; flagella directed outside; becomes parenchymula.
• What is the defining characteristic of the class Calcarea?

  Spicules made of CaCO3 only
• What is the defining characteristic of the class Hexactinellida?

  1. rayed spicules of silica and chitin
• What is the defining characteristic of the class Demospongiae?

  Largest class with spicules and fibers of silica and spongin/chitin
• What is the defining characteristic of the class Homoscleromorpha?

  Lack of spicules and a clear distinct basal membrane
• What are the two distinct layers of Placozoa?

  A thin upper layer and a ventral layer with columnar flagellated cells.
• What is Treptoplax reptans?

  A species first described from Naples, Italy in 1896 but has not been seen again.
• What is T. adhaerens?

  A species first discovered on the walls of a marine aquarium in Australia in 1883.
• What is the significance of the fluid-filled space between the layers of Placozoa?

  It contains a contractile network of fibrous cells.
• What is the asexual reproduction method in Placozoa?

  Methods include budding, fragmentation, and binary fission.
• What is the regenerative capacity of Placozoa?

  They have a high regenerative capacity.