Kamptozoa and Bryozoa are two phyla of small aquatic invertebrates. They are related to snails and clams (collectively called mollusks), bristleworms, earthworms, and leeches (collectively called annelids), and ribbon worms (nemertea). But their precise position on the tree of life, and how closely related they are to these other animals, has always puzzled evolutionary biologists. Previous studies have consistently moved them around. What's more, while Kamptozoa and Bryozoa were originally considered to form one group, they were separated based on their appearance and anatomy.