While the Endangered Species List sounds pretty straightforward—it’s a list of species at risk for extinction—you may not know just how complicated nominating, assessing, and registering these at-risk flora and fauna can be.

It’s Endangered Species Day, so now is as good a time as any to dive into the fascinating politics that go into protecting wildlife under the powers of the Endangered Species Act of 1973. In the latest edition of The Brain Scoop, a YouTube series from the Field Museum in Chicago, host Emily Graslie details just what distinguishes threatened and endangered species, how species get on the list, how they’re prioritized by the U.S. Fish and Wildlife Service, and just how much animal charisma comes into play. For the record, there are 90 clams on the list, even if the term “endangered species” might conjure up an image of a panda or a tiger rather than a mollusk.

Images: YouTube