As the planet’s most expansive ecosystem, the deep sea can be a tough place to find a mate. Though, scientists say, some deep-sea anglerfishes evolved a unique method of reproduction that ensures that once they land a partner in the vast open waters, they remain latched for life.

These anglerfishes, called ceratioids, reproduce through sexual parasitism, in which the tiny males attach to their much larger female counterparts to mate. In some species, the males bite the females and then release once the mating process is complete. In others, the male permanently fuses to the female. In a process called obligate parasitism, the male’s head dissolves into the female and their circulatory systems merge. He transforms into a permanent sperm-producing sexual organ.