Facetotectans (aka y-larvae) have been a mystery since their discovery in the 1800s. Scientists are unsure of what they grow up to become, but we now know where these crustaceans fit in the tree of life. This image shows a cypris larvae, or y-cyprid. Credit: Niklas Dreyer Y-larvae, mysterious crustaceans related to barnacles, may be parasitic and are key to understanding barnacle evolution. When most people think of barnacles, they imagine shell-like organisms clinging to boats, docks, or even whales. Yet some barnacles go far beyond passive attachment — they can actually invade and take over their hosts. “Instead of...