The argonaut, the only cephalopod to secrete and live in a shell of its own making, is a unique sea creature that swims via jet propulsion – using powerful jets of water squirted through a funnel in its shell.
Male argonauts tend to grow to up to a few centimeters in length, only about 10% of the size of the females, which can reach up to 2 meters long, depending how much they grow their shells.
This sexual dimorphism poses an obvious question – how is reproduction possible when your potential baby daddy is only a fraction of your size?
It’s been found that argonauts have an interesting way of resolving the little issue of copulation. And although live male argonauts have never actually been observed in the wild, an understanding of their reproduction processes has been gleaned from observing a dead male and a live female.
The tiny male throws a modified arm containing spermatozoa (called a hectocotylus) at the female, which will then swim toward the female's mantle (the sac which stores her organs), finding its way inside and subsequently fertilizing the eggs. A female's eggs can actually be fertilized by more than one hectocotylus by storing them in the mantle cavity.
The male's modified arm develops in a pouch under its eye until it’s called upon, at which points it explodes out of the cavity and swims across to the female, attaching itself to her mantle via suckers, and wiggling its way inside.
Sounds sexy right?
Males will die after throwing their tentacle at the female. However, unusually for cephalopods, the females don’t die after laying eggs. Instead, they continue to grow and reproduce.
[H/T The Independent]