Look up "anglerfish reproduction". The males are tiny and permanently fuse themselves to a female, basically becoming a parasite of balls.
Wikipedia:
When a male finds a female, he bites into her skin, and releases an enzyme that digests the skin of his mouth and her body, fusing the pair down to the blood-vessel level. The male becomes dependent on the female host for survival by receiving nutrients via their shared circulatory system, and provides sperm to the female in return.
It’s really quite an amazing adaptation. These fish live at extreme depths. There is essentially no light at all down there, apart from the dim glow of the bioluminescent bulbs they use for luring prey. I would imagine encounters between males and females of the species to be quite rare under the circumstances. That the male can permanently attach himself to the female is a very tidy solution to the problem.