Speaking of fish....
I was on another forum discussing Alpaca sex, which is extraordinary in that the male deposits directly into the uterus, rather the vagina, with a huge level of pain for his Alpaca lady. (Alpaca sex is a normal thing to chat about, right? Right?)
But that is not what I am here for. I am here for Anglerfish. Those deep sea fish that use bioluminecsence to capture prey.
This are fish with a strong sexual dimorphism, the males are way, way smaller than females.
The method of reproduction down in the deep dark ocean makes it hard to find a lover. So female Anglerfish do the obvious and absorb the male into their cloaca to live as a parasitic sperm donor. The males basically become more than just a parasite, more like a chunk of male flesh within the body of the female, just able to supply sperm. I mean, who of us wouldn't?
Deep-sea anglerfish that fuse to mate lack genes involved in the body’s response against pathogens or foreign tissue.
www.sciencenews.org