CHAPTER 28 Flashcards
Evolution of animals
All animals are multicellular and heterotrophic
They ingest whole foods and digest internally
Lack a cell wall
Are mobile and have muscles and nerves
Reproduce sexually and have a diploid lifecycle
Monophyletic (Both vertebrates and invertebrates)
The colonial flagellate hypothesis
Animals are descended from an ancestor resembling a hollow spherical colony of flagellated cells
Individual cells within the colony become specialized
Two tissue layers could have arisen by infolding of certain cells into a hollow sphere
Implies that radial symmetry proceeded bilateral symmetry
Evolution of body plans
All of the diversified body plans characteristic of animals today were present by the Cambrian period
Slight shift in the DNA code an expression of certain genes sponsorable for the differences that arise during development.
Symmetry
Asymmetric- no particular body shape
Radial symmetry- body organized circularly
Bilateral symmetry- definite right and left halves
Embryonic development
The first tissue layer that appears in embryonic development is called germ layers
They give rise to organs or organ systems
Diploblastic- two tissue layers ectoderm and endoderm found in Cnidarians
Triploblastic- three tissue layers ectoderm mesoderm and endoderm
They are either protostomes or deuterostomes
- Protostomes first embryonic opening becomes the mouth
Deuterostomes. Second embryonic opening becomes the mouth
Protostomes vs deuterostomes
Cleavage- cell division immediately after fertilization
Protostomes- spiral cleavage determinate fate( will die if separated)
Deuterosomes- radial cleavage indeterminate fate
Protostomes sit in valley of original cells deuterostomes stack up on top of the original cells
Three basic kinds of body plans for triploblastic animals
Acoelomates- no body cavity
Pseudocoelomates- body cavity between mesoderm and endoderm called pseudocoelom
Coelomates- body cavity entirely within the mesoderm called the coelom.
