Paper nautilus or great nautilus (Argonauta argo). It is not closely related to the nautilus, and its name relates to a paper-like shell (fan-shaped, left) that is only produced by the females. The female is twenty times the size of the male, with the spiral shell’s single chamber serving the purpose of protecting her eggs. Without the shell it resembles a floating octopus. It feeds on plankton and other small organisms, near the surface of the open ocean in warm and tropical regions. Photographed in the French Mediterranean.