As we’ve seen, invertebrates include a broad scope of animals, from the simplest of animals—the sponges—to the complex arthropods and annelids. As you review the phyla we’ve discussed in this lesson, remember the characteristics that set apart each phyla. Remember: animals are grouped together based on their structure and appearance.

Simple Animals

This video introduces us to the “simplest” of the animals. We differentiate animals by the number of tissue layers they have, and by the complexity of those layers.

Complex Animals

This video continues our exploration of invertebrates. We discuss the more complex annelids and arthropods.