The greater argonaut (Argonauta argo) is a pelagic octopus known for its sexually dimorphic nature, where females are significantly larger than the males. Females produce a delicate, thin, coiled "shell" or egg case to protect their eggs, using specialized arms to secrete calcium. They live in warm, tropical, and subtropical waters worldwide, near the surface, where they use air trapped in their shell to control buoyancy. These skilled hunters capture small crustaceans, molluscs and other prey with their tentacles and can change color to camouflage themselves.