Revealing the origin and evolutionary history of the world’s manifold life forms is one way in which we seek to understand them. Even the smallest creature can yield fascinating insights. For example, take the Dicyemida, which are microscopic parasites that live inside cephalopods such as octopuses and cuttlefish. These seemingly inconsequential beings have baffled taxonomists due to their simple body structure, which is composed of around 40 cells and does not include many common body elements such as a circulatory system. Historically, researchers have disagreed about the Dicyemida’s classification, including their closest relatives and on which rung of the evolutionary ladder they are situated.