Argonauts and their detachable phallus

The species of Octopus known as Argonaut is quite a unique species in its self. Being the only extant genus in the family Argonautidae. They can be found throughout the world in tropical waters. They also display extreme sexual dimorphism, where females will reach sizes of up to 50cm including their shell.(depending on which species) but males will only reach a size of 2cm and lack a shell (Finn and Norman., 2010). The males also lack dorsal tenticals which on the female is used to create the egg case AND males also obtain a detachable penis. 

Photo credit: Finn and Norman 2010, (a) female argonaut (Argonauta nodosus),
 (b) chambered nautilus (Nautilus pompilius)

 When copulation occurs, males will use their detachable penis which is called a hectocotylus, and insert it into the females palliative cavity. Once the penis is inserted he then detaches himself from the hectocotylus leaving it inserted within the female. 
Sadly after the male performs this unusual technique he will die afterwards, whereas the female is able to house and store the detachable penis full of sperm for weeks until her eggs are fully developed for reproduction. She can lay thousands of eggs which can consist of three different developmental stages. The eggs are incubated in a type of shell produced by the female until hatching occurs (V. Laptikhovsky and A. Salman., 2002).

References :

• Finn, J.K. & Norman, M.D. 2010, "The argonaut shell: gas-mediated buoyancy control in a pelagic octopus", Proceedings: Biological Sciences, vol. 277, no. 1696, pp. 2967-2971.

• Laptikhovsky, V. & Salman, A. 2003, "On reproductive strategies of the epipelagic octopods of the superfamily Argonautoidea (Cephalopoda: Octopoda)", Marine Biology, vol. 142, no. 2, pp. 321-326.