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Winged paper nautilus (Argonauta hians):  Komodo, Indonesia. Photo: Bvanant (iNaturalist) Enlarge Image!

Contents

• Introduction
  
  
• Description
  • The Shell
  • Palaeontology
    
    
• Ecology and Behaviour
  • The Hectocotylus
    
    
• Species and Distribution
  
  
• Links

Introduction

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The paper nautiluses (Argonautidae) are a rather remarkable and curious family of cephalopods. The name "paper nautilus" might suggest that they are relatives of the chambered nautiluses (Nautilida), a very ancient group of cephalopods which, unlike most living cephalopods, still possess a coiled external calcareous shell and outwardly resemble fossil ammonites more than modern octopuses or squids. In Japanese, however, paper nautiluses are also known as Kaidako (貝蛸), which literally means "shell octopus".

Class Cephalopoda Cuvier, 1795 Superorder Octopodiformes Order Octopoda Suborder Cirrata Suborder Incirrata Superfamily Argonautoidea Family Argonautidae Argonauta argo Linnaeus, 1758 Argonauta hians [Lightfoot], 1786 Argonauta nodosus [Lightfoot], 1786 Argonauta nouryi Lorois, 1852 Superfamily Octopodoidea Family Octopodidae: z.B. Octopus vulgaris Linnaeus, 1758 Source: MolluscaBase (2025): Argonautidae Cantraine, 1841, simplified.

In reality, paper nautiluses have no close relationship to the nautilus apart from the fact that both belong to the cephalopods. In fact, paper nautiluses resemble octopuses much more closely than any other cephalopod group. As their classification demonstrates (see simplified diagram on the right), they are indeed related to octopuses, since they belong to the same order, the Octopoda. This relationship is also evident in their external appearance, as paper nautiluses, unlike nautiluses, only have eight arms at their disposal. Nevertheless, paper nautiluses display a number of unusual features that distinguish them from all other octopus-like cephalopods, which explains their placement in their own superfamily within the finless octopuses (Incirrata).

According to MolluscaBase (2025), only four extant species of the family Argonautidae are recognised today, all belonging to the genus Argonauta, whereas all other genera and species are extinct. Fossil argonauts, however, are not easily found, probably because their delicate shell-like structure is too fragile to be readily preserved. Fossil remains are known from the Oligocene (approximately 23 - 34 million years ago; see geological timescale), but are particularly known from Miocene deposits (approximately 5.3 - 23 million years ago) in Japan, Cyprus and Styria (Austria).

Description

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Female Greater Paper Nautilus (Argonauta argo): Teneriffa, Canary Islands. Photo: Marc Martin Sola (iNaturalist). Enlarge Image!

Drawing of a paper nautilus by C. Merculiano in Jatta, G. (1896): "I Cefalopodi viventi nel Golfo di Napoli". (Link, Source).

Among living paper nautiluses, the Greater Paper Nautilus (Argonauta argo) is the largest species, with its shell-like eggcase reaching up to 30 cm in length.

Paper nautiluses exhibit pronounced sexual dimorphism: while the female may grow to a body length of up to 10 cm, the male rarely exceeds 2 cm. Only the female produces a shell-like structure, constructing an eggcase of up to 7 cm shortly before reaching sexual maturity, which serves as a container for her eggs. Males, by contrast, do not produce such a structure. The Greater Paper Nautilus can be distinguished from other paper nautilus species by the characteristic bluish colouration of the two anterior arms and the area surrounding the eyes. In addition, the shape and surface structure of the eggcase are commonly used for species identification.

Argonauta argo belongs to the octopuses (Octopoda), as indicated by the presence of eight arms, each bearing two rows of suckers. This contrasts, for example, with a nautilus, which possesses a much larger number of appendages (up to 90), but these lack suckers. The paper nautilus is a pelagic cephalopod, unlike most of its octopus relatives, which primarily inhabit the ocean floor. It is now assumed that paper nautiluses diverged relatively early in their evolutionary history from the remaining predominantly benthic octopuses (Octopoda). They may therefore have retained certain ancestral features of early octopus lineages. Further clarification is expected from DNA studies.

The scientific name Argonauta derives from Greek mythology. The legend of the Argonauts tells of a group of Greek heroes, led by Jason, who set out in search of the Golden Fleece in Colchis in the Caucasus, travelling aboard the exceptionally swift ship Argo. Until the 19th century, it was believed that the specially modified arms of the female argonaut functioned as sails, allowing the animals to move with the aid of the wind in a manner somewhat similar to the Portuguese man o'war (Physalia physalis). However, unlike the mythical Argo, the sail-like arm ends of the female argonaut do not serve locomotion. Instead, they are used in the construction of the eggcase through glandular cells located in them.

Bizarre Beasts: The Only Octopus With a  Shell. ( YouTube Video).
Em Gems: The Paper Nautilus, An Octopus in Disguise. ( YouTube Video).
Sea Change: Argonaut Encounter. ( YouTube Video).

The Shell

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	Who Was Jeanne Villepreux-Power? The French naturalist Jeanne Villepreux-Power (1794–1871) studied the local flora and fauna during the years she lived in Sicily. Her particular interest was in molluscs: She investigated paper nautiluses (Argonauta argo) in aquaria of her own design and construction, and was able to demonstrate, among other things, that the eggcase is produced by the female argonaut itself, and that the sail-like expanded arm tips serve for the construction and repair of the eggcase rather than for locomotion. She corresponded with numerous male scholars of her time and was, for example, recognised in 1858 by Richard Owen for her contributions to experimental zoology - a highly unusual distinction for a woman in that period. Source: C. Arnal: Jeanne Villepreux-Power - A Pioneering Experimental Malacologist. The Malacologist 34 (Malacological Society of London).		Egg case of the Greater Paper Nautilus (Argonauta argo): Milazzo, Mes- sina, Sicily, Italy. Photo: Andrea Ruggieri (iNaturalist)  Enlarge Image!

Paper nautiluses owe their common name to the unusual shell-like eggcase produced by the female as a container for her brood. This structure is formed with the aid of glandular cells located in the sail-like expanded tips of two specialised arms. There are differing views regarding the timing of eggcase formation. It was traditionally assumed that the female begins producing the eggcase shortly before reaching sexual maturity. More recent evidence, however, suggests that the female may only begin constructing the eggcase after the eggs have been fertilised, with the structure continuing to grow until the young hatch (Kamatsos et al., 2025, see below).

One small specimen of Argonauta argo was observed carrying 48,800 embryos within an eggcase measuring only 88 mm in length. The largest known eggcase of Argonauta argo, however, has been measured at 300 mm, although such dimensions may represent exceptional cases. The eggcases of argonauts are relatively variable in form, which historically led to the description of numerous additional species. These are now regarded as junior synonyms, leaving only four extant species recognised today.

Okutani, T.; Kawaguchi, T. (1983): "A mass occurrence of Argonauta argo (Cephalopoda: Octopoda) along the coast of Shimane Prefecture, Western Japan Sea". Venus 41: p. 281 - 290.

In addition, female argonauts are capable of repairing damage to the eggcase. Unlike the shells of molluscs such as bivalves or snails, the eggcase is not permanently attached to the soft body. Whereas shells in these groups are connected through retractor or adductor muscles, the female argonaut instead holds the eggcase using several of her arms. The eggcase of paper nautiluses is also composed of calcite rather than aragonite. Furthermore, unlike the shell of a nautilus, it is not chambered. Nor does the eggcase play any direct role in locomotion.

Although air is enclosed within the upper part of the eggcase and contributes to buoyancy, and it has been suggested that the female may replenish this air reserve at the water surface when necessary, no gas exchange takes place between the soft body and the eggcase. Instead, the paper nautilus moves by means of the jet propulsion mechanism typical of most cephalopods, expelling water from the mantle cavity through the funnel. The characteristic shape and surface structure of the eggcase may help improve hydrodynamic properties; it has also been suggested that the eggcase may provide some protection against ultraviolet radiation from sunlight, to which argonauts, unlike their benthic relatives, are exposed to a greater degree.

The eggcase of the paper nautilus is therefore not homologous to the true shell of molluscs, but rather represents a completely different and independently evolved structure with a different function: protecting the eggs rather than the animal itself. Since it is not attached by retractor muscles, the animal is also able to leave the eggcase if necessary.

Palaeontology

Argonauta joanneus, a fossil Argonaut from the Miocene of Styria (Austria). Source: Hilber, V. (1915).

The characteristic eggcase of argonauts probably first appeared during the Paleogene, approximately 23 - 66 million years ago (see geological timescale), when octopus-like cephalopods began to shift from a benthic lifestyle, as still seen in modern octopuses, towards an epipelagic mode of life. Fossil argonaut eggcases are, however, relatively uncommon, probably because the thin-walled structure is poorly suited to fossil preservation. Even recently washed-up argonaut eggcases are often found in a heavily damaged condition.

The oldest fossil evidence of argonauts and their relatives comes from the Oligocene deposits of Japan (approximately 23 - 34 million years ago). Obinautilus pulcher was initially regarded as a fossil nautilus species, but is now generally assigned to the argonaut lineage. It was not until the Miocene (approximately 5.3 - 23 million years ago) that a greater number of argonaut fossils became known. In addition to discoveries from Japan, California and Cyprus, this includes the species formerly described as Argonauta joanneus from Wetzelsdorf near Preding in Styria (Austria). During the Miocene, present-day Styria was covered by a marginal sea connected to the ancient Tethys Ocean, the so-called Paratethys.

		Hilber, V. 1915: "Der älteste bekannte und erste miozäne Argonauta". Mitteilungen des naturwissenschaftlichen Vereins für Steiermark 51: 107–110. (PDF).
		Martill, D.M.; Barker, M.J. (2006): "A Paper Nautilus (Octopoda, Argonauta) From the Miocene Pakhna Formation of Cyprus". Palaeontology, Vol. 49, Part 5, S. 1035 - 1041 (PDF).
		Saul, L.R.; Stadum, C.J. (2005): "Fossil Argonauts (Mollusca, Cephalopoda, Octopodida) From the Late Miocene Siltstones of the Los Angeles Basin, California". Journal of Paleontology, 79 (3): S. 520 - 531 (2005). (Link).

Ecology and Behaviour

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Winged Paper Nautilus (Argonauta hians, presumably juvenile female without shell) on a pelagic jellyfish: Mabini, Batangas, Philippines. Photo: Xenomatt (iNaturalist) Enlarge Image!

In contrast to their predominantly bottom-dwelling relatives, the true octopuses, paper nautiluses or argonauts are epipelagic animals that inhabit the upper, sunlit layers of the ocean close to the surface. Here they prey upon crustaceans, salps, pelagic snails such as pteropods (Pteropoda), and other pelagic organisms. The eggcase also serves the female argonaut as a buoyancy aid. Although it is not chambered like the shell of a nautilus, it contains air, which the female may even replenish at the surface when necessary. Unlike in the nautilus, however, no gas exchange takes place, and locomotion is achieved solely by the typical jet propulsion mechanism of cephalopods.

In the open ocean, argonauts have occasionally been found associated with jellyfish. The animals do not simply consume the jellyfish itself; rather, they may bore into its body and feed on food particles present within the jellyfish's stomach. It has also been suggested that the argonaut may use the jellyfish for camouflage, defence, and perhaps even as a means of transport.

Heeger, T.; Piatkowski, U.; Möller, H. (1992): "Predation on jellyfish by the cephalopod Argonauta argo". Marine Ecology Progress Series. 88: S. 293 - 296. (PDF).
Robert Stansfield: A crazy night of argonauts. (Facebook Video).

Observations of female Argonauta argo in captivity have shown that the animals also employ their sail-like expanded arm tips during feeding. When prey comes into contact with these modified arms, it is rapidly seized by one of the remaining arms (Norman, 2000).

Along the coasts of South Africa and Australia, mass strandings of abandoned argonaut eggcases occasionally occur. These events are seasonal and generally take place between April and August, towards the end of the breeding season, presumably after the adult animals have died following the hatching of the young.

Der Hectocotylus

Argonauta nodosus, male with visible hectocotylus. Northland, New Zealand. Photo: Paul Craiger (iNaturalist) Enlarge Image!

Hectocotylus of Argonauta argo. Source: Battaglia et al. (2021).

The dwarf male of the paper nautilus is distinguished particularly by its greatly modified third arm, which remains enclosed in a sac until it is used. As in other cephalopods, this specialised arm, transformed into a reproductive organ, is referred to as a hectocotylus and is used to transfer a spermatophore to the female.

Unlike other cephalopods, however, the male argonaut detaches the hectocotylus during copulation (autotomy), after which it is capable of finding its own way into the mantle cavity of the female. Since no male argonauts with regenerated hectocotyli have ever been found, this suggests that the male probably dies after mating.

This also explains why Georges Cuvier, who discovered such a structure within the mantle cavity of a female argonaut, initially described it in 1829 as a separate species. The true nature of the hectocotylus was only understood several years later.

Battaglia, P.; Stipa, M.G.; Ammendolia, G.; Pedà, C.; Consoli, P.; Andaloro, F.: Romeo, T. (2021): "When nature continues to surprise: observations of the hectocotylus of Argonauta argo Linnaeus, 1758". The European Zoological Journal, 88 (1), 980 - 986. (Link).

Species and Distribution

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The four presently valid extant species of the Argonauta genus. (Source, modified and corrected). Enlarge Image!

Paper nautiluses are distributed worldwide in tropical and subtropical waters. In the Mediterranean, however, they are encountered only occasionally and are considered relatively rare (Kamatsos et al., 2025). Four extant species are currently recognised (see above), of which the Greater Paper Nautilus (Argonauta argo) is the largest and probably the best known.

The four currently recognised living species of the genus Argonauta are:

• Greater Paper Nautilus (Argonauta argo): The eggcase is compressed in shape. The keel is narrow and covered with two rows of small nodules. The wall of the eggcase is light and relatively closely and finely ribbed. The aperture is thickened and may terminate in horn-like projections. Argonauta argo occurs predominantly in tropical and subtropical waters throughout the world. Smaller forms occur only occasionally and rather rarely in the Mediterranean ( Wikipedia).
  
  
• Winged or Brown Paper Nautilus (Argonauta hians): The keel of the eggcase is broad and bears small rounded nodules along its margin. The wall is ribbed at greater intervals than in Argonauta argo. The aperture possesses a wing-like expanded margin. However, Argonauta hians is highly variable, and at least two forms have been described: a northern form occurring around Taiwan, Hong Kong and Japan, and a southern form occurring around the Philippines and the South China Sea. The latter, for example, lacks the wing-like expansion of the aperture ( Wikipedia).
  
  
• Knobbed Paper Nautilus (Argonauta nodosus): The eggcase is reinforced with numerous small nodules on both the keel and the ribs. Argonauta nodosus is relatively widespread throughout the Indo-Pacific region but occurs only south of the equator. It is most commonly encountered in southern Australia, New Zealand and South Africa ( Wikipedia).
  
  
• Noury's Paper Nautilus (Argonauta nouryi): Noury's Paper Nautilus possesses an elongated eggcase, which appears more oval than those of the other argonaut species. Argonauta nouryi is best known from waters along the western coast of North and Central America, ranging from Panama to Baja California, although it has also been recorded in the south-western Pacific, including the Coral Sea. Argonauta nouryi is considered the rarest species of paper nautilus and is therefore highly sought after by shell collectors  ( Wikipedia).

Links

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• Kamatsos, E.; Chaniotaki, M.E.; Zevgolis, Y.G. (2025): "Rare Observation of a Female Argonauta argo in the Northeastern Aegean Sea: A Contribution to Mediterranean Cephalopod Records". Diversity 2025, 17(5), p. 361 (Link).
• Norman, M.: "Cephalopods - A World Guide. Pacific, Indian Ocean, Red Sea, Atlantic Ocean, Caribbean, Artic, Antarctic". Conchbooks, Harxheim, 2000; p. 190 - 191. (Link).
• Wikipedia: Argonauta argo.

Latest Change: 31.05.2026 (Robert Nordsieck).
Latest Link Check: 24.05.2026.