Radix sp. The two larger specimens shown here are preparing to mate. Each of these snails is a hermaphrodite. Both have a complete set of male and female reproductive structures. The snail on top will act as the male during the coming copulation. After copulation is completed, the two snails will change positions, and the previous female-acting snail will then become the male-acting partner, and vice versa.
John B. Burch (photographer; copyright holder), Mollusk Division, Museum of Zoology, University of Michigan-Ann Arbor