Did you know that all Paper Nautilus shells are from Argonauta argo females?
Commonly referred to as Paper Nautilus, Argonauta argo (Octopoda - Argonautidae) is a species of cephalopod with a very particular sexual dimorphism.
The female is lodged in a boat-shaped, unchambered shell that serves primarily as brood chamber (also called egg case). This thin-walled, transversely-wrinkled shell is secreted by lobular enlargements at the tips of the dorsal arms. Female egg cases tend to be longer than female mantle lengths, so individuals can often recede completely inside the structure
The male is dwarf, about one twentieth the size of a female; males can only reach a maximum of several centimeters in length while females can be two meters long.
Another distinctive feature of males is that they lack of shell, so all shells of the species are from females. Occasionally whole mature males are found in the shell of the female.
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Photo credit: ©Xavi Simona | Locality: unknown (2009)