II. Origins of Diversity

A. Earth's Early Inhabitants

B. Origins of Multicellular Eukaryotes

C. The Cambrian Explosion

D. The Fossil Record

III. Animal Characteristics

A. Animal Cells Are Bordered by a Cell Membrane

B. Animals Are Heterotrophs

C. Animals Typically Move at Some Stage in Their Lifecycles

D. Adults Are Diploid and Often Undergo Sexual Reproduction

IV. Classifying Animals

A. Binomial Nomenclature in Taxonomy

1. Classification Categories (Species to Kingdom)

B. Tissue and Organ Levels of Organization and Germ Layers

1. Gastrulas Possess Endoderm and Ectoderm

2. Animals Develop as Either Protostomes or Deuterostomes

3. Mesoderm

4. The Coelom

C. Symmetry

1. Radial Versus Bilateral Symmetry

2. Cephalization

3. Larval Symmetry Sometimes Differs From That in Adults

D. Overview of Animal Classification

V. Invertebrate Phyla

A. Porifera (Sponges)

1. Sponges Are an Ancient and Unusual Phylum

2. Sponge Characteristics

3. Sponge Reproduction

B. Cnidaria and Ctenophora (Cnidarians and Comb Jellies)

1. Tissue Level of Organization

2.  Cnidarians Have Radial Symmetry and Possess Specialized Stinging Cells

3. Cnidarian Body Forms and Reproduction

4. Ctenophores (Comb Jellies) Exhibit Biradial Symmetry and Several Unique Features

C . Platyhelminthes (Flatworms)

1 . Bilateral Symmetry and Organ Level of Organization

2 . Specialized Flatworm Structures

3 . Fluke and Tapeworm Lifecycles

4 . Flatworm Reproduction

1. Rotifers and Nematodes Are Pseudocoelomates Having a Tube Within a Tube Body Plan

2. Rotifer and Nematode Lifestyles and Characteristics

3. Rotifer and Nematode Reproduction

E. Mollusca (Mollusks)

1. Mollusks Are Coelomates

2. Variations in Mollusk Classes

3. Features Common to All Mollusks: the Foot, the Mantle, and the Visceral Mass

4. Mollusk Reproduction

F. Annelida (Segmented Worms )

1. Annelid Body Plan and Segmentation

2. Variations in Annelid Classes

3. Annelid Reproduction

G. Arthropoda (Insects, Spiders, and Crustaceans)

1. Arthropods Have Specialized and Fused Segments

2. Characteristic Arthropod Features: Jointed Appendages and Exoskeletons

3. Specialized Arthropod Senses and Organ Systems

4. Arthropod Reproduction

H. Protostomes and Deuterostomes Differ Greatly

1. Coelom Formation

2. Spiral, Determinate Cleavage Versus Radial, Indeterminate Cleavage

I. Echinodermata (Echinoderms)

1. Radially Symmetrical Adults Develop From Bilaterally Symmetrical Larvae

2. The 'Spiny-Skinned' Echinoderms Have Endoskeletons

3. Echinoderm Water Vascular System and Tube Feet

4. Echinoderm Reproduction

J. Chordata (The Invertebrate Chordates)

1. Definitive Chordate Characteristics

2. Urochordata (The Tunicates and Sea Squirts)

3. Cephalochordata (The Lancelets)

VI. Economic Roles of Invertebrates

VII. Conclusion