Chp 3

• Phylum porifera


  • Believed to be one of the most primitive metazoan animals
  • Lack organs and most typical animal features
  • No head, mouth or gut cavity
  • Body is immobile
• General characteristics of phylum porifera

  • Radial symmetry or absence of symmetry
  • Body with many pores, canals or chambers through which water flows
  • No true tissues, organs, movable parts or appendages
  • No digestive or circulatory systems, rely on water flow to obtain food, oxygen and remove wastes
  • Intracellular digestion
  • Asexual and sexual reproduction
  • No obvious sensory or nerve cells, but different types of other cells exist
• Cell types


  • Choanocytes - cells with cylindrical or conical collars surrounding one flagellum, drive water flow
  • Ostia - channels leading to the interior through the mesohyl, controlled by porocytes
  • Pinacocytes - plate-like cells forming external skin, digest large food particles
  • Lophocytes - amoeba-like cells that secrete collagen
  • Collencytes - collagen-producing cells
  • Rhabdiferous cells - secrete polysaccharides
  • Oocytes and spermatocytes - reproductive cells
  • Sclerocytes - secrete mineralized spicules
  • Spongocytes - secrete spongin, a fibrous material
  • Myocytes - conduct signals and cause contraction
  • Grey cells - act as immune system
  • Archaeocytes - totipotent amoeba-like cells with roles in feeding and clearing debris
• Water flow


  1. Intake at bottom, ejection from osculum at top

  2. Can control flow by closing osculum and ostia, varying flagella beat

  3. Flexibility of layers and remodeling of mesohyl allow shape adjustment
• Body structure


  • Asconoid - tube or vase shape, limited size
  • Syconoid - pleated body wall with flagellated chambers, larger size
  • Leuconoid - interior filled with mesohyl containing network of chambers, largest size
• Skeleton


  • Mesohyl functions as endoskeleton, stiffened by mineral spicules or spongin fibers
  • Spicules may be made of silica or calcium carbonate, vary in shape
• Asexual reproduction


  Internal and external budding, gemmules in freshwater sponges

  
• Sexual reproduction


  1. Hermaphroditic, sperm produced by choanocytes, eggs from archaeocytes

  2. Four types of larvae, all mobile balls of cells that settle and attach
• Classification of sponges


  • Calcarea (Calcispongiae) - spicules of calcite, asconoid to leuconoid body forms
  • Hexactinellida (Glass sponges) - spicules of silicate, hexaxons, leuconoid body form

  
• Phylum Porifera

  • Lack a nervous system, reactions are largely local
  • Coordination depends on transmission of messenger substances by diffusion, wandering amoeboid cells, and along fixed cells in contact