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.

Phylogeny:  Noury’s Argonaut (Lorois, 1852), is a Cephalopod that is a member of the Argonautidae Family of Argonauts. The genus Argonauta is the only genus in this family, and there are four species in this genus. They are also known as the Paper Nautilus, the Rough-keeled Argonaut and the Long Argonaut and in Mexico as Argonauta Común and Casa de Caballo.

Morphology: Noury’s Argonauts are a part of a group of pelagic octopuses that collectively have been called Paper Nautili. The females secrete a paper-thin egg case that is utilized to rear families and for camouflage, protection, and defense. Noury’s Argonauts have a rounded body with eight tentacles and no fins. 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. Two of the tentacles are webbed and used for food collection. They have very large eyes.. The female Noury’s Argonaut reaches 10 cm (3.9 inches) in length and males are about one-third the size of the females. The “shells” are made of calcite and 7% magnesium carbonate, with a three-layer construction. Unlike nautilus shells, they lack the gas-filled chamber, and are not a true cephalopod shell, being an evolutionary innovation unique to the genus. The chamber traps surface air to maintain buoyancy and is utilized as a brood chamber. The 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. The shells are thin and brittle.  The shells 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. The males do not have shells. Noury’s Argonaut can be easily confused with the Paper Nautilus, Argonauta cornutus (less elliptical; depth that is 58% to 62% of length) and the Pacific Argonaut, Argonauta Argo (shortened shell that has a depth that is 68 to 72% of its length).

Habitat and Distribution: Noury’s Argonaut is a pelagic species that spends its entire life at, or near, the surface of the open sea, and 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. 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 California Sur between January and March.

Diet: Noury’s Argonauts are suspension feeders that use their tentacles to capture , crustaceans, jellyfish, planktonic mollusks and salps.

Predation: Noury’s Argonauts are prey for many organisms including billfishes, sea birds, other cephalopods, dorado, lancetfish, marine mammals, and tunas.

Reproduction: Noury’s Argonauts are gonochoric ( male or female for life) and reproduce sexually, with internal fertilization. Mating occurs when the male inserts his hectocotylus into the female’s mantle.  The hectocotylus breaks off inside the female, where it fertilizes her eggs. Females are known to contain more than one hectocotylus at any one time obtained from different males. Females may also maintain eggs in three stages of development at any one time.

Ecosystem Interactions: The commensal, parasitic, commensal, or symbiotic relationships of Noury’s Argonaut has not been formally documented..

Human Interactions: Noury’s Argonaut shells are prized and deemed to be of great interest and value to shell collectors although they are extremely fragile. From a conservation perspective they considered to be of Least Concern.

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