Biodiversity Of Animals

• Symmetry

  Occurs when an animal can be cut into one or more planes to obtain two mirror images
• Examples of phyla

  • sponges
  • jellyfish
  • blue bottles
  • corals
  • sea anemones
  • flatworms (e.g. Planaria, bilharzia worm, tapeworm)
  • roundworms
  • earthworms
  • sea worms
  • leeches
  • snails
  • oysters
  • mussels
  • octopi
  • starfish
  • sea urchins
  • insects
  • spiders
  • crustaceans
  • myriapoda
  • fish
  • amphibians
  • reptiles
  • birds
  • mammals
• Nematoda, Mollusca, and Echinodermata are only mentioned in this module whereas it goes into more detail on the other six phyla
• Radial symmetry

  Animals that can be cut in more than one vertical plane through its centre to obtain two mirror images
• Bilateral symmetry

  Animals that can only be cut in one vertical plane through its centre to form two mirror images
• Body plan

  A set of morphological characteristics (shape and structure) of an animal's body, as well as the way in which it develops
• Important features when classifying animals

  1. Symmetry and cephalisation

  2. Number of tissue layers that develop in the embryo

  3. Presence or absence of a coelom and a blood system

  4. Number of openings in the digestive tract
• Approximately 30 phyla in the animal kingdom

  • Porifera
  • Cnidaria
  • Platyhelminthes
  • Nematoda
  • Annelida
  • Mollusca
  • Echinodermata
  • Arthropoda
  • Chordata
• Kingdom Animalia can be divided into two main groups

  • Invertebrates (animals without a vertebral column)
  • Vertebrates (animals with a vertebral column)
• Scientists use body plans to classify animals into groups (phyla)
• Asymmetry

  Animals that show no symmetry are asymmetrical
• All bilaterally symmetrical animals are triploblastic with three germ layers and an organ level of organisation
• Disadvantage of radial symmetry is that locomotion is slow and inefficient
• The coelom separates the digestive tract from the body wall
• Classification of animals based on germ layers

  • Diploblastic
  • Triploblastic
• Methods of locomotion enabled by cephalisation

  • Crawling
  • Swimming
  • Running
  • Burrowing
  • Flying
• Ectoderm

  Outer protective layer, nervous system, and sense organs
• Tissue layers in the embryo

  • Ectoderm- outer germ layer
  • Endoderm- inner germ layer
  • Mesoderm- germ layer between ecto- and endoderm
• Bilaterally symmetrical animal


  • Has a definite dorsal (top) and ventral (bottom) side, a left and right side, an anterior and a posterior end
• All the different tissues and organs of an animal develop from the three germ layers
• Types of triploblastic animals based on coelom presence

  • Coelomate
  • Acoelomate
  • Pseudocoelomate
• Mesoderm

  Coelom and blood system
• The fluid that occurs in the coelom is known as coelomic fluid
• Bilateral symmetry

  An animal can only be cut in one vertical plane through its centre to form two mirror images
• Triploblastic animals are more advanced and complex than diploblastic animals
• Mesoglea

  Non-cellular jelly layer separating ectoderm and endoderm in some animals
• Cephalisation

  Concentration of nerve cells at the anterior end of the body in bilaterally symmetrical animals
• Diploblastic animals do not have a coelom
• Endoderm

  Epithelial lining of the digestive tract
• Body plans of different phyla

  • Porifera
  • Cnidaria
  • Platyhelminthes
  • Annelida
  • Arthropoda
  • Chordata
• Acoelomate has no cavity (coelom) in the mesoderm
• A fluid-filled coelom can act as a hydrostatic skeleton
• Due to the separation of the digestive tract from the body wall by mesoderm tissue in triploblastic animals, there was a need for a transport system
• Ingestion is the intake of food
• Digestion in these animals is therefore a discontinuous process
• Different regions in the digestive tract become specialised to improve efficiency, e.g. a stomach for digestion and an intestine for absorption
• A blood system developed in most triploblastic animals for the transport of O₂, CO₂, and digested nutrients as well as an excretory system to transport waste products
• Biological importance of a coelom
• Pseudocoelomate has a coelom, but it is not seen as a 'true' coelom because it is not only surrounded by mesoderm tissue
• The presence of a coelom allows animals to reach a considerable size and become more complex by providing space for organs to develop