BIO 182 Chapter Notes - Chapter 44.1-44.2: Bilateria, Eumetazoa, Diploblasty
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44. 1 a tree of life for more than a million animal species. Anatomy and morphology provide the basis for finding evolutionary relationships between species. Animal definition: heterotrophs get carbon and energy from organic molecules, embryos gastrulate, multicellular. A trait that is present in more species most likely evolved earlier. Evolution of animals: multicellularity, gastrulation, and collagen, sponges branch off, tissues are formed, two branches form. Bilaterians bilateral symmetry and complex organs. Three groups of bilaterians: acoelomates no body cavity, pseudocoelomates primitive body cavity, coelomate body cavity (coelom) Species that have very different adult forms may develop in similar ways which suggests a common ancestor. Cnidarians: two germ layers endoderm and ectoderm, diploblastic, radially symmetric. Bilateria: tripoblastic, bilaterally symmetric, three germ layers endoderm, mesoderm, and ectoderm. Many early hypotheses of evolutionary relationships were later supported by molecular sequencing. 44. 2 the simplest animals: sponges, cnidarians, ctenophores, and placozoans.
