Porifera

• Sponges are sessile, multicellular animals with no true tissues or organs.
• The body plan of sponges consists of an outer layer called choanocyte chambers, which contain flagella used to move water through the sponge.
• Phylum Porifera


  • Animals lacking tissues (and therefore organs) and a definite symmetry
  • 7000 marine species; 150 freshwater species
  • Among the most abundant animals in the deep ocean
  • Most members lack symmetry
  • Various growth forms - larval sponges free-swimming, adults remain attached - sessile
• Cell types in sponges

  Truly multicellular
• Sponge body structure


  1. Water comes in ostia, through spongocoel, exits osculum

  2. Mesohyl - middle layer, gelatinous matrix, spicules - needles of calcium carbonate or silica, spongin - reinforcing tough protein fibers

  3. Choanocytes - collar cells, flagellated, contribute to water circulation, face internal cavity, engulf and digest food from passing water
• Sponge body types


  • Ascon
  • Sycon
  • Leucon
• Sponge reproduction


  1. Asexual - fragmentation

  2. Sexual - choanocytes transform into sperm, sperm captured and passed to egg cell in mesohyl, development may occur within mother or in open water, larva is planktonic, will settle and transform into adult
• Sponge classes

  • Class Calcarea
  • Class Hexactinellida
  • Class Demospongae
• Phylum Cnidaria


  • Most marine, few fresh water species
  • Diploblastic
  • Bodies have distinct tissues but no organs
  • No reproductive, circulatory, or excretory systems
  • No concentrated nervous system - latticework of nerve cells, touch, gravity, light receptors
• Nematocysts


  Used by cnidarians to capture prey, secreted within nematocyte, mechanism of discharge unknown, some carry venom
• Cnidarian body forms


  • Polyps - cylindrical and sessile
  • Medusa - umbrella-shaped and free-living
• Choanocytes have flagella at one end to create water currents through the canal system.
• Calcarea is a type of sponge characterized by their spicules made up of calcium carbonate.
• Sponges are filter feeders that trap food particles from the water flowing through their canals.
• Hexactinellida is a class of sponges with hexagonal silica spicules as their primary structural elements.
• Water enters the sponge through the ostia and flows through the canal system, where it encounters the choanocytes.
• The choanocytes in sponges form a network of channels called ostia, which lead into larger chambers called oscula.