A species of octopus loses its penis during sex.
The Argonaut octopus has a lot of sex, but it never directly experience sex.
This is because it reproduces via tele-sex. The male octopus produces sperm in its penis.
The penis is then detached (yes, detached) from the body and swims (yes, swims) by itself to a suitable female.
The female is automatically impregnated by this detached, swimming penis.
The most the male can do is sit back and watch as his disembodied junk carries out the sex out for him.
After all of this, the male begins to regrow his penis, which is often a very slow, tedious process.