Chapter 32 An Introduction to Animal Diversity

Characteristics of Animals Animals are: Multicellular Heterotrophs Eukaryotic Have tissues and differentiated cells Eat Reproduce and Develop 1.3 millions species have been identified, estimates of 10 to 200 million exist

Early Embryonic Development Sperm and egg meet through fertilization to form a zygote The zygote undergoes mitosis, called cleavage A blastula, or multi-celled hollow ball forms These cells form tissue layers that make up a gastrula

Eras of Animal Life Neoproterozoic Era (1 B  542 mya): First fossilized animals are from this time period. Paleozoic Era (542  251 mya): the Cambrian explosion occurs, huge diversity of animal species, including vertebrates, evolve Mesozoic Era (251  65.5 mya): animal life spreads across the planet Cenozoic Era (65.5 mya  present): dinosaurs, birds, and mammals all evolve

Body Plans A body plan is a set of traits that make up an organism. A group of animals that share the same level of organizational complexity is known as a grade. There are 4 main characteristics: Symmetry Tissues Body Cavities Development

Symmetry Animals can have radial symmetry, in which the parts of an animal radiate out from the center (starfish) Or they can have bilateral symmetry, with equal left and right sides (lobsters, humans) Animals with a distinct forward facing head at the top of the body have gone through cephalization.

Tissue Layers The tissue layers of an animal embryo are called germ layers, and form organs. The ectoderm is the outermost layer and forms the skin and nervous system. The endoderm is the inner layer of the embryo and turns into the digestive system, liver, and lungs. Bilaterally symmetrical animals have a third layer, called the mesoderm, which forms the other body organs and muscles.

Body Cavities Some animals have body cavities, a fluid-filled space that separates the digestive tract from the outer body wall, this is called a coelom. Pseudocoelomates have a body cavity that is formed from a different type of tissue (not mesoderm). Acoelomates do not have body cavities.

Development Protostomes, like worms and bugs, develop a mouth first during fetal development. Deuterostomes, like people and starfish, develop an anus before they develop mouths.