Overview of Animal Diversity

1. Overview of Animal Diversity Chapter 31

2. General Features of Animals • Heterotrophs • Multicellular • Able to move from place to place • Diverse in form and habitat • Sexual reproduction • Characteristic embryonic development

3. Diverse Kingdom • Traditional classification of animals • multicellular animals, metazoans, traditionally divided into 35 distinct phyla • First branch - tissues • Parazoa lack definite symmetry and do not possess tissues or organs. • Eumetazoa have definite shape and symmetry and usually have organs and organ systems.

5. Traditional Classification of Animals • Second branch - symmetry • Eumetazoan branch has two principles branches. • Radiata - radial symmetry • Bilateria - bilateral symmetry • Further branches were assigned by comparing key shared features of the body plan. • body cavity • coelom

6. Broad Groupings of Kingdom Animalia

7. Key Transitions in Body Plan • Evolution of tissues • first key transition in animal body plan • Evolution of bilateral symmetry • radial symmetry - regular arrangement of parts around central axis • bilateral symmetry - right and left halves form mirror images • dorsal vs. ventral • anterior vs. posterior

8. Radial and Bilateral Symmetry

9. Bilateral Symmetry • Bilaterally symmetrical eumetazoans produce three germ layers. • ectoderm • endoderm • mesoderm • Much of the nervous system is in the form of major longitudinal nerve cords. • ultimately led to evolution of definite head • cephalization

10. Three Body Plans

11. Key Transitions in Body Plan • Evolution of a body cavity • Presence of a body cavity allows digestive tract to be larger and longer. • storage of undigested food • more complete digestion • more space for gonads to expand

12. Key Transitions in Body Plan • Kinds of body cavities • acoelomates - no body cavity • pseudocoelomates - possess pseudocoel • coelomates - possess coelom

13. Coelomates • Coelom poses circulation problem • solved by circulatory system • open circulatory system • Blood passes from vessels into sinuses, mixes with body fluid, and reenters vessels in another location. • closed circulatory system • Blood is physically separated from other body fluids and can be separately controlled.

14. Key Transitions in Body Plan • Advantages of a coelom • Allows contact between mesoderm and endoderm, so that primary induction can occur during development.

15. Key Transitions in Body Plan • Evolution of deuterostome development • mitotic egg division leads to blastula • indents to form blastopore, opening to the archenteron • Bilaterians can be divided into protostomes (mouth-first) and deuterstomes (mouth-second).

16. Protostome and Deuterostome Differences • Cleavage • spiral • radial • Fate of embryonic cells • determinate - predetermined fate • indeterminate - identical daughter cells • Fate of blastopore • mouth or anus develops near blastopore • Formation of coelom

17. Embryonic Development

18. Key Transitions in Body Plan • Evolution of segmentation • advantages • Each segment may go on to develop a more or less complete set of adult organs. • Locomotion is far more effective when individual segments can move independently due to flexibility of movement.

19. Animal Classification is Being Reevaluated • New look at metazoan family tree • New taxonomical comparisons using molecular data have come to new, different conclusions. • hint that key morphological characters used in traditional classification are not necessarily conservative • Molecular systematics uses unique sequences within certain genes to identify clusters of related groups.

20. Roots of the Animal Family Tree • Origins of metazoans • Most taxonomists agree the animal kingdom is monophyletic. • Three prominent hypotheses exist for origin from single-celled protists. • multinucleate hypothesis • colonial flagellate hypothesis • polyphyletic origin hypothesis • debate over cause of Cambrian explosion