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 brood of one zillion eggs, just above the surf line at Km 21, Cabo Real, Baja California Sur, April 2004. Size: 10 cm (3.9 inches). Shell 4.2 cm (1.7 inches) x 2.8 cm (1.1 inches). Note: in collection of this species, I was fooled badly, originally believing that a standard octopus had taken up residence in a discarded shell. Only when I removed the “octopus” from the shell did I discover the brood of eggs. An excellent photo opportunity was lost! I also collected two additional Paper Nautilus shells adjacent to this collection, but both shells were empty.
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 Long Argonaut Shell, the Paper Nautilus Shell and the Rough-keeled Argonaut Shell and in Mexico as Argonauta Común and Casa de Caballo.
Morphology: The Noury’s Argonaut Shell has an elliptical profile 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 to 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. Noury’s Argonaut can be easily confused with the Greater Argonaut, Argonauta argo (shortened shell that has a depth that is 68 to 72% of its length).
The Noury’s Argonaut Shell is 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 males do not have shells.
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.
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. They are an Eastern Pacific species that 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.
Ecology and Behavior: Noury’s Argonauts are suspension feeders that use their tentacles to capture , crustaceans, jellyfish, planktonic mollusks and salps. They are prey for many organisms including billfishes, sea birds, other cephalopods, dorado, lancetfish, marine mammals, and tunas. 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. Their engagement in any type of commensal, parasitic, or symbiotic relationships has not been formally doucumented. From a conservation perspective they considered to be of Least Concern. Noury’s Argonaut Shells are prized and deemed to be of great interest and value to shell collectors although they are extremely fragile.
Synonyms: Argonauta conradi, Argonauta cornutus, Argonauta expansus, and Argonauta gruneri.