Body Plans

• Body plan


  A structural characteristic of an organism that separates it from other organisms or groups of organisms
• The relationship between the body plan and mode of life of each phylum is important when looking at the diversity found within the animal kingdom
• These characteristics are used to determine which phylum to place an animal in
• Important features of body plans

  • Symmetry and cephalisation
  • Number of tissue layers developing from the embryo
  • Presence or absence of a coelom
  • Presence or absence of a through gut

  
• Symmetry and cephalisation


  • There are three types of symmetry: Asymmetry, Bilateral symmetry, Radial Symmetry
  • Animals that have bilateral symmetry are usually more advance and have cephalisation
  • Cephalisation - The presence of a definite head that contains sense organs, feeding appendages and the brain

  
• Symmetry and cephalisation


  • Asymmetry - Amoeba, Sponges
  • Radial symmetry - Cnidaria
  • Bilateral symmetry - All other phyla except Porifera and Cnidaria

  
• Diploblastic


  Animals that only have two primary germ layers (ectoderm and endoderm) in the embryo
• Triploblastic


  Animals that have three tissue layers (ectoderm, endoderm and mesoderm) in the embryo

  
• Animals with radial symmetry produce two tissue layers - diploblastic

  
• Animals with bilateral symmetry produce a third tissue layer - triploblastic

  
• Coelom


  A large fluid-filled cavity that lies between the body wall and internal organs
• Coelom


  • Allows more complex organs to develop - muscular system, blood system etc.
  • Animals without a coelom are called Acoelomate
• Through gut


  A gut that runs from mouth to anus
• Through gut


  • Allows digestion and excretion of more complex molecules - allows animals to grow larger and move into more diverse environments
  • Animals with only one opening (blind-ending gut) are limited in the amount of food they can consume
• Gut types


  • One opening (blind-ending) gut - Cnidarians or Platyhelminthes
  • Two opening (through) gut - All other animal groups
• Protostomes are characterized by their embryonic development, where the mouth develops first from the blastopore (mouth) and then the anus forms later on.
• Chordates possess a notochord, which is a flexible rod made up of cartilage or bone that extends along the backbone.
• The phylum Chordata includes vertebrates such as humans, fish, birds, reptiles, amphibians, and mammals.