Anglerfish

We bet some women wish sex worked this way for humans as well! For the longest time, scientists were confused because they simply couldn't seem to catch a male anglerfish, until they figured out the reason. Born tiny, weak and dependent, the male anglerfish just never seem to catch a break in life. Since they are born without a digestive system, they are forced to find a female quickly and bite on her flesh.

This then releases an enzyme, which digests the male's skin and he ends up becoming nothing but a lump in the side of the female. Then, when she's ready to spawn, her 'male appendage' is already available ready to release sperms into her egg as an when required!