Noury’s Argonaut and Shell, Argonauta nouryi

Noury’s Argonaut, Cephalopod and Shell, Argonauta nouryi. Collected on the beach in its own shell (pictured above) with a large brood of eggs, at Agua Verde, Baja California Sur, March 2019. Length: 11.4 cm (4.5 inches). Shell: 4.8 cm (1.9 inches) x 1.9 cm (0.7 inches). Collection and photograph of Barry Mastro, Escondido, California.

Noury’s Argonaut, Argonauta nouryi (Lorois, 1852), is a Cephalopod that is a member of the Argonautidae Family of Argonauts, that is commonly known as the Paper Nautilus, the Rough-keeled Argonaut and the Long Argonaut and in Mexico as argonauta común and casa de caballo.

Noury’s Argonaut Shell is elliptical in outline and is more elongate than most species in the Family having a depth that is only 53% to 57% of its length. The shell is ribbed and the keel (outer margin) is knobbed with a smooth but grainy surface. The shell is cream colored with brown along the oldest portion of the keel. They are octopus-like and dimorphic with separate sexes. The female Noury’s Argonaut reaches 10 cm (3.9 inches) in length and can generate a calcareous egg chamber that resembles a shell that can be up to 5.8 cm (2.3 inches) in length, 3.2 cm (1.3 inches) in height, and 2.5 cm (1.0 inch) in width being not as wide as tall. These shells are thin, brittle, and moderately well hinged with one chamber that is involutely coiled. The early part of the coil is moderately well hinged. The males are about one-third the size of the females and do not have “shells”.

Noury’s Argonauts is a pelagic species that spends its entire life at, or near, the surface of the open sea, at depths up to 21 m (70 feet). They are vertical migrators that move to the shelter of the bottom at night and move toward the surface at night for feeding. They have eight tentacles, two of which are unique, and web-like, used to collect food. The male can be differentiated from the female by the existence of an altered third tentacle (the hectocotylus) that it keeps in a pouch until it is needed for reproduction. Following fertilization, the male will die.

Noury’s Argonaut can be easily confused with the Paper Nautilis, Argonauta cornutus (less elliptical; depth that is 58% to 62% of length) and the Pacific Argonaut, Argonauta pacificus (shortened shell that has a depth that is 68 to 72% of its length).

Noury’s Argonaut has global distribution. In the Eastern Pacific they range from Southern California to Peru and are found in all Mexican waters of the Pacific Ocean. They are found washed up on the beaches most frequently in Southern Baja between January and March.

Synonyms include: Argonauta conradi, Argonauta cornutus, Argonauta expansus, and Argonauta gruneri.

These shells are prized and deemed to be of great interest and value to shell collectors.