Two Cephalopods of the Argonautidae Family can be found in this website:
Phylogeny: Argonaut Shells of the Argonautidae Family (Linnaeus, 1758), are Cephalopod mollusks in the Octopoda order, just like other octopuses. The Argonautidae Family is one of four families in the superfamily Argonautoidea. Argonauta is the only genus in this family, and it consists of four species.
Description: Argonauts are 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 and defense. Argonauts have a rounded body with eight limbs and no fins. They have very large eyes and small webs between the tentacles. They have a funnel-mantle locking apparatus that consists of a knob like cartilage in their mantle and corresponding depressions in the funnel. Their beaks have a small rostrum and a sharp shoulder. The shells are laterally compressed, double keeled and fringed by two rows of alternating tubercles. The sides are ribbed with either flat centers or with winged protrusions. They 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. Only the females of the genus form a shell. The shell is unlike the shells of gastropods in that it is not secreted by the mantle. Instead, it is secreted, and held on to, by two specially modified arms that are widened at the tips, having a sail-like appearance. The shells consist of a coil, having no spire. The shell is single chambered. The female lives in the shell, protecting the eggs from predator attack until they hatch. The females can be up to eight times larger than the males. Females can reach 10 cm (4.0 inches) in length and have shells that are 30 cm (12 inches) in length while the males reach a maximum of 2.0 cm (0.8 inches) and do not make shells.
Habitat and Distribution: Argonauts are pelagic, spending their entire lives at, or near, the surface of the open sea. The females are normally found with their head and tentacles protruding from the shell, but she can withdraw into the shell for protection. The males have been found within salps. They have the ability to move up and down in the water column, however they are limited in their depth range, with most found in the first 30 m (100 feet) of the water column. Argonauts are found worldwide in subtropical and tropical waters. At least three species are found in Mexican waters.
Natural History: Argonauts feed diurnally on small crustaceans, mollusks, jellyfish, and salps. They have the ability to use their radula to drill into shelled prey, and then inject toxin. In turn they are preyed upon by billfishes, dorado, longsnouted lancetfish, tunas, sea birds, marine mammals, and other cephalopods. They have the ability to change color and blend into their surroundings to avoid predation. They also have the ability to produce ink which is utilized to help avoid predation. Mating occurs when the male inserts a modified arm into the female’s mantle. This arm functions as a reproductive organ, called a hectocotylus. 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 Females raise many broods, while males mate once and have short lifespans. The females have been documented in the literature for centuries, while males were only described in the late 19th century. They have the ability to swim with locomotion provided by expelling water through their funnels. Females are sometimes found holding on to one another, forming chains of up to twenty individuals. Otherwise, Argonauts are generally individualistic. Mass strandings of hundreds of individuals on widely distributed beaches has been well documented. Argonauts are seldom found, but based on the number of strandings, and the number found in the stomachs of predators, they are thought to be abundant. The argonaut has been the subject of both classical and modern art and utilized in jewelry, pottery, and architecture. They are also featured in the Jules Verne’s Novel Twenty Thousand Leagues Under the Sea, however, in mythical size. The name of the genus Argonauta, is of mythical Greek origin. The Argonauts were a group of Greek heroes, led by Jason in the 6th century BC, that traveled in the Argo to Kolchis in the Black Sea the home of Medea and the Golden fleece. In Greek, Argonaut means “one who travels on the Argo.” This refers to these animals behavior of sailing in their shells.