Argonauta argo

Warm temperate and tropical seas around the world.

Likes to be near the surface of the water. It is an epipelagic oceanic species.

The maximum length of shell is 30 cm in females, but only 1.5-2 cm in males. The shell is coiled and laterally compressed with a narrow keel and numerous sharp nodules. Nodules toward the center of the coil are brown, but most of the shell is white.

The male uses a specialized arm called a 'hectocotylus' to fertilize the eggs. The hectocotylus is inserted into the females pouch and breaks off during mating. The female forms a "nacelle," a thin calcareous shell, with two of her legs (the others are used for swimming). This structure holds the eggs throughout development.

The female is up to twenty times larger than the male. Normally these animals are solitary.

Feeds on plankton and small organisms on the surface of the water.

Can be found in fish markets in India and Japan. The shell is praised by collectors because of its beauty, coloration, sculpture, and fragility.

This animal is very common but is rarely spotted by humans. Every once and a while many of them may be washed up by a change in currents or chased into shallow waters by predators, allowing people to observe and catch them.

The species is heavily preyed upon by tunas, billfishes, and dolphin.