This document discusses how animals can be classified in multiple ways, including by their physical features, where they live, and how they act. It then focuses on classifying animals based on whether they have backbones or not. For vertebrates with backbones, it describes the main groups of fish, amphibians, reptiles, birds, and mammals based on their defining characteristics. For invertebrates without backbones, it outlines groups like sea jellies, worms, mollusks, and arthropods. Finally, it briefly discusses how different animals are born from eggs or through live birth.