Argonautidae

The Argonautidae is a family of octopods within the order Octopoda, known for their unique external shell, which is produced only by the females. This thin, coiled, and fragile shell serves as a protective structure and is absent in males, who are significantly smaller and lack a shell entirely. This distinguishing feature sets them apart from other cephalopods in the order Coleoidea, such as squids and most octopuses, which either have internal shells or no shell at all. Argonauts are pelagic, meaning they live in open water rather than on the seafloor, and are commonly found in warm, tropical oceans. They also exhibit marked sexual dimorphism, with females being much larger than males. Reproductively, the male uses a specialized arm to transfer sperm into the female’s mantle cavity, after which the female carries fertilized eggs in her shell until they hatch.