An Introduction to Animal Diversity

1. An Introduction to Animal Diversity • Chapter 32

2. Characteristics of Animals • Multi-cellular • Heterotrophic eukaryotes - ingestion • Lack cell walls – collagen • Tissues that develop from embryonic layers • Most have nervous & muscular tissue • Most reproduce sexually • Flagellated sperm • Large egg • Diploid zygotes • Diploid stage dominates the life cycle • Some animals have larvae • Immature form • Undergoes metamorphosis • Animals share Hox genes • Unique homeobox containing a family of genes that play an important role in development

3. Development • Zygote undergoes a series of mitotic cell divisions calledcleavage • An eight cell embryo is formed by three rounds of cell division • In most animals, cleavage results in the formation of a multicellular stage called a blastula. • Hollow ball of cells that surround a cavity called the blastocoel

4. Development • Most animals also undergo gastrulation, a process in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues • The ectoderm (outer layer) • The endoderm (inner layer)

5. Development • The pouch formed by gastrulation, called the archenteron, opens to the outside via the blastopore • The endoderm of the archenteron develops into the tissue lining the animal’s digestive tract • Becomes the mouth in protostomes • Becomes the anus in deuterostomes

6. Animals are characterized by “body plans” • No symmetry, no true tissues -Sponges • Radial symmetry • Jellyfish • Organisms where you can cut through the central axis and produce a mirror image • Bilateral symmetry • Lobsters, humans, etc. • Organisms that have a right and left side. • A cut in half would divide them into two mirror image halves • Dorsal – back • Ventral – belly • Anterior – head • Posterior - tail

7. Animals are characterized by “body plans” • Cephalization • Sensory equipment at one end of the organism (usually the anterior) • Acoelomates • Flatworms • Have no cavities between their alimentary canal and the outer wall of their body • Pseudocoelomates • Triploblastic (three tissue layers) • Cavity formed from mesoderm and endoderm • Coelomates • True coelom (body cavity filled with fluid) • Space separates the digestive tract from the outer body wall • Coelom forms from tissue derived from mesoderm only • Functions of the body cavity • Cushion and suspend organs • Hydrostatic skeleton • Enable internal organs to grow and move independently

8. Protostomes and Deuterostomes • Cleavage • Protostomes – spiral and determinate • Deuterostomes – radial and indeterminate • Coelom formation • Protostomes – forms from splits in the mesoderm • Deuterostomes – mesodermal outpocketings of the archenteron • Blastopore • Protostomes – mouth • Deuterostomes – anus, mouth forms from secondary opening

9. Characteristics of Animals • Lack symmetry and true tissues? • Show radial symmetry and are diploblastic? • Have three tissue layers but lack a body cavity? • Show bilateral symmetry and have a pseudocoelom? • Have a true coelom and are protostomes? • Have a true coelom and are deuterostomes? If you can group the animal phyla based on these characteristics, you will be prepared for the most common type of animal questions on the AP exam.