BCB705 Biodiversity: Chapter2 - Evolution of Biodiversity

Table of Contents

1. THE INFINITE VARIETY: THE BEGINNING OF LIFE
2. BUILDING BODIES: INVERTEBRATES OF THE OCEANS
   1. Fossil History of Marine Invertebrates
   2. Platyhelminthes: the building block for other invertebrates
   3. Platyhelminthes: a surprisingly diverse group
   4. Annelids: the first segmented animals
   5. Brachiopods: developing a bivalve shell
   6. The first Molluscs
   7. The Molluscs diversified
   8. Molluscs: Feeding mechanisms
   9. Molluscs: Evolving and keeping the shell
   10. Molluscs: Secondary loss of the shell
   11. Echinoderms: Penta-symmetrical creatures of the oceans
   12. Echinoderms: A hydrostatic structure
   13. Echinoderms diversity: variations on a theme
   14. Arthropoda: the most successful animal phylum
   15. Arthropoda: Segmentation the successful formula
   16. Early Arthropods: The fossil record
   17. Living descendents of the Trilobites
   18. Crustaceans: Arthropod success in the sea
   19. Arthropod Exoskeleton: Evolving to occupy land
   20. Test Yourself
   21. Assignments
3. THE FIRST FORESTS
4. THE SWARMING HORDES
5. THE CONQUEST OF THE WATER AND THE BIRTH OF THE VERTEBRATES
6. THE INVASION OF THE LAND
7. A WATER-TIGHT SKIN AND THE SHELLED EGG
8. LORDS OF THE AIR
9. EGGS, POUCHES AND PLACENTAS
10. THEME AND VARIATION
11. THE HUNTERS AND THE HUNTED
12. A LIFE IN THE TREES
13. THE COMPULSIVE COMMUNICATORS

Platyhelminthes: the building block for other invertebrates

Simpler animals than those first found in the fossil records still inhabit the earth and its oceans and their ancestors may have represented the predecessors for the shelled invertebrates that are found in the fossil records. These soft-bodied animals belong to the phylumPlatyhelminthes. The most basic of these animals is the flatworm, a flat-leaf shaped worm which like jellyfish have a single opening to their gut through which food is ingested and waste is ejected. Their bodies have differentiated into three layers, the ectoderm, mesoderm and endoderm. Cells with a different structure and function have aggregated to form a primitive system (e.g. nervous system which consists of a network of nerve fibres). Nevertheless, they have no breathing system with oxygen diffusing directly through the skin. Their undersides are covered with cilia which, by beating, permits them to glide over surfaces. Their front end has a mouth on the under-surface and a few light sensitive spots above.

Flatworms
Scientific classification
Kingdom: Animalia Subkingdom: Eumetazoa Superphylum: Platyzoa Phylum: Platyhelminthes