Argonauts: astronauts of the sea

The beautiful paper-thin constructions of octopuses in the genus Argonauts, sometimes called paper nautiluses, are not true shells like those of other molluscs, but the female octopus' eggcase.

They have been known since antiquity but it wasn’t until French marine biologist Jeanne Villepreux-Power (1794-1871) invented the aquarium and observed argonauts that their true nature was revealed.

The shells or eggcases are constructed by the female's specialised webbed arms. The structures act as floating brood chambers for the argonaut’s eggs which remain inside until they are hatched. Argonauts are not attached to these shells as other molluscs are to theirs.

While most octopuses dwell at the sea-bottom, argonauts use their shells to float in the water column. This mechanism wasn’t observed until 2015, when it was revealed that argonauts propel themselves to the surface of the water and rock in their shells until a ‘gulp’ of air is taken into the eggcase. This air is then trapped with part of their body to maintain the required buoyancy.

Many of the shells in the Museum’s collection were donated by women. They are a rare part of the collection that is exclusively of female specimens, and also pioneered by women researchers, with many women donors.