Hitchhiking fish that are famous for suctioning themselves to other marine animals have a very unexpected hiding place: the rear ends of manta rays, a new study finds.

These fish, known as remoras (family Echeneidae), frequently get free rides when they use their suction discs ‪—‬ modified backs, or dorsal fins ‪—‬ to latch onto marine animals like sharks, whales and sea turtles. It has generally been thought that remoras provide a cleaning service to the animal they are traveling with, picking parasites off their skin. But this new discovery shows that this relationship might not always be beneficial to the manta rays.