At the beginning of this module, we looked at the sea sponge, which isn’t exactly the first thing that comes to mind when you hear the word animal, which may be due to the fact that sponges were the first to branch away from the rest of the Animal Kingdom on the evolutionary tree. Despite their early divergence from other animals, they still have several shared characteristics with rest of the Animal Kingdom:

• All animal species are multicellular
• All animal species are heterotrophic
• All animal species lack cell walls
• All animal species produce sperm cells

Most animals share these other notable features that sponges lack:

• Most animal species have tissues
• Most animal species have organs
• Most animals have body symmetry

While these shared characteristics serve as foundational similarities, there is incredible diversity among animals (as we learned in Module 9: Animal Diversity)—all you have to do is look at the differences between yourself and a sponge to see the range of features within the Animal Kingdom.