Chapter 32

An Introduction to Animal Diversity

Characteristics of AnimalsAnimals are:MulticellularHeterotrophsEukaryoticHave tissues and differentiated cellsEatReproduce and Develop1.3 millions species have been identified,

estimates of 10 to 200 million exist

Early Embryonic DevelopmentSperm 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 LifeNeoproterozoic 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 PlansA 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:SymmetryTissuesBody CavitiesDevelopment

SymmetryAnimals 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 LayersThe 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 CavitiesSome 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.

DevelopmentProtostomes, like

worms and bugs, develop a mouth first during fetal development.

Deuterostomes, like people and starfish, develop an anus before they develop mouths.