When it is mature, the male's digestive system degenerates, making him incapable of feeding independently, which necessitates his quickly finding a female to prevent his death. The sensitive olfactory organs help the male to detect the pheromones that signal the proximity of a female.
When he 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 then atrophies into nothing more than a pair of gonads, which releases sperm in response to hormones in the female's bloodstream indicating egg release.
This extreme sexual dimorphism ensures that, when the female is ready to spawn, she has a mate immediately available.