Argonauta argo

Argonauta argo, also known as the ‘Greater argonaut’, is a species of pelagic octopus belonging to the genus Argonauta.
It is the largest species in the genus and also produces the largest eggcase. The eggcase is characterised by two rows of small, sharp tubercles running along a narrow keel, smooth ribs across the walls of the shell, and a thickening along the shell aperture, which forms distinct protrusions or ‘horns’ on either side.

Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Coleoidea
Superorder: Octopodiformes
Order: Octopoda
Suborder: Incirrata
Superfamily: Argonautoidea
Family: Argonautidae
Genus: Argonauta
Species: Argonauta argo

From my collection

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