From Biol301

What is an Animal?

• It's hard to come up with a good definition, but here are some usually correct criteria:

1. Multicellular, heterotrophic (being incapable of synthesizing required organic materials from inorganic sources) eukaryotes.
2. Body held together by protein; lack hard cell walls of plants
3. Have nervous and / or muscle tissue.
4. Usually sexual reproducing with a diploid stage in most life cycles.

• See lecture from 03/29/06 for more information on how to define an animal.
• See image on page 636 or 640 for a good cladistic explanation of animal diversity
  • First specialized tissues came about in Eumetazoa
  • Second symmetry split: radial symmetry in Cnidarias (jellies, etc.) and bilateral
  • The next split we spoke of in class was the proto- vs. deutero- stone split (mouth first vs. anus first)
• Cephalization = "an evolutionary trend toward the concentration of sensory equipment on the anterior end...."