1. The argonaut octopus
2. Dolphins
3. Flatworms
4. Giraffes
5. Bed bugs
Honourable mentions because nature is extra
- Slugs: Some species have penises longer than their entire bodies. Mating involves twisting into a knot of slime and occasionally chewing off a stuck penis if things go wrong.
- Anglerfish: The tiny male bites the female and fuses into her body — literally becoming a permanent sperm donor, losing his eyes and organs.