''Argonauta argo'', also known as the greater argonaut, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...

belonging to the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

'' Argonauta''. The Chinese name for this species translates as "white sea-horse's nest". ''A. argo'' was the first argonaut species to be described and is consequently the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

of the genus. The

type specimen In biology, a type is a particular wiktionary:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to a ...

of ''A. argo'' was collected in the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...

and is deposited at the

Linnean Society of London The Linnean Society of London is a learned society dedicated to the study and dissemination of information concerning natural history, evolution, and taxonomy. It possesses several important biological specimen, manuscript and literature colle ...

Description

''A. argo'' is the largest species in the genus and also produces the largest eggcase. Live animals have a characteristic blue sheen on the first

arm In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...

pair and around the eyes. The eggcase is characterised by two rows of small, sharp

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection ...

s running along a narrow keel, smooth ribs across the walls of the shell, and a thickening along the shell aperture, which forms distinct protrusions or 'horns' on either side. ''Argonauta cygnus'' Monterosato, 1889 was described based on a shell which lacked these protrusions, although it is now considered a

junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...

of ''A. argo''. The greatest recorded size of an ''A. argo'' eggcase is 300 mm. A damaged

beak The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food ...

of a female ''A. argo'' (ML = 40.0 mm; caught at ), measuring 4.3 mm in hood length and 7.8 mm in crest length, is mentioned in ''A Handbook for the Identification of Cephalopod Beaks''.

Distribution and habitat

''A. argo'' is cosmopolitan, occurring in

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

and

subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...

waters worldwide. A dwarf form exists in the

, which was described as ''Argonauta argo mediterranea'' Monterosato, 1914, although this

taxon In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

is now regarded as invalid.

Biology

The female of the species, like all

argonaut The Argonauts (; Ancient Greek: ) were a band of heroes in Greek mythology, who in the years before the Trojan War (around 1300 BC) accompanied Jason to Colchis in his quest to find the Golden Fleece. Their name comes from their ship, ''Argo'', n ...

s, creates a paper-thin eggcase that coils around the octopus much like the way a

nautilus The nautilus (, ) is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in ...

lives in its

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...

, hence the name paper nautilus. ''A. argo'' is thought to feed primarily on pelagic

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

s. The species is preyed on by numerous predators. It has been reported in the stomach contents of '' Alepisaurus ferox'' from the south-western Pacific. Papierboot Argonauta 200705181139

Males of this species reach

sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definitio ...

at a mantle length (ML) of 8 mm. Females mature at about double the size of ''

Argonauta bottgeri ''Argonauta bottgeri'', also known as Böttger's argonaut, is a species of pelagic octopus belonging to the genus '' Argonauta''. The female of the species, like all argonauts, creates a paper-thin eggcase that coils around the octopus much like ...

'' and '' Argonauta hians''. They begin to secrete an eggcase at 6.5–7.0 mm ML. Eggs are usually laid when females reach 14–15 mm ML, although the size at which this takes place differs across the animal's range. A small ''A. argo'' residing in an 88 mm long eggcase was estimated to be carrying 48,800 embryos. Females grow to 100 mm ML, while males do not exceed 20 mm ML. In the open ocean, ''A. argo'' has been observed attached to

jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...

. This behaviour has been known for a long time, although little was understood about the relationship prior to the work of Heeger ''et al.'' in 1992. In "Predation on jellyfish by the cephalopod ''Argonauta argo''", Heeger ''et al.'' describe their observations of a female ''A. argo'' found atop a host jellyfish. The argonaut was seen holding on to the

aboral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

(exumbrellar) surface of the jellyfish using its lateral and ventral arms. The authors found that about half of the animal's aboral surface was damaged and large pieces of

mesoglea Mesoglea refers to the extracellular matrix found in cnidarians like coral or jellyfish that functions as a hydrostatic skeleton. It is related to but distinct from mesohyl, which generally refers to extracellular material found in sponges. Desc ...

were missing, presumably removed by the argonaut. Additionally, two holes, apparently bite marks, were found in the center of this area with channels leading from these holes into the gastral cavity of the jellyfish. The argonaut presumably used these channels to suck food particles from the gastral cavity. Heeger ''et al.'' suggested that "the association provided shelter or camouflage for the argonaut". Observations of captive ''A. argo'' females suggest that the expanded webs of the dorsal arms may aid the animal in feeding. Mark Norman mentions, "when food was touched against the spread webs, an arm shot out of the shell in a sweeping action, grabbing the prey". Argonauts are not thought to actively hunt, but employ this method to catch animals that bump into them in the open ocean. ''A. argo'' is occasionally involved in mass strandings along the

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

n and southern

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

n coastlines. The strandings are seasonal and generally occur between April and August, towards the end of the animals' spawning season.

Culture

In Japanese, this species is called "Aoi-gai" (

kanji are the logographic Chinese characters taken from the Chinese family of scripts, Chinese script and used in the writing of Japanese language, Japanese. They were made a major part of the Japanese writing system during the time of Old Japanese ...

: 葵貝,

Katakana is a Japanese syllabary, one component of the Japanese writing system along with hiragana, kanji and in some cases the Latin script (known as rōmaji). The word ''katakana'' means "fragmentary kana", as the katakana characters are derived f ...

: アオイガイ n Japanese and English/ref>), which means "Shell of Aoi" (not ''

Malva ''Malva'' is a genus of herbaceous annual, biennial, and perennial plants in the family Malvaceae. It is one of several closely related genera in the family to bear the common English name mallow. The genus is widespread throughout the temper ...

'' but '' Asarum caulescens''). Japanese have compared two eggcases of argonauts lapped each other to a leaf of ''Asarum caulescens''. Another name is "Kaidako" (

: 貝蛸 or 貝鮹,

: カイダコ), which means "Shell Octopus".

Gallery

File:Argonauta argo eggcase.png, Eggcase of ''A. argo'' File: Argonauta argo upper beak (side view).jpg, Upper beak of a female File: Argonauta-argo-001.jpg, One of the earliest known depictions of ''A. argo'', from ''Index Testarum Conchyliorum'' (1742) by

Niccolò Gualtieri Niccolò Gualtieri (9 July 1688 – 15 February 1744) was an Italian doctor and malacologist. He established a private natural history collection, and catalogued its contents, the best known being of the molluscs. Gualtieri was born in Florenc ...

File: Argonauta argo.jpg , Illustration of a female ''A. argo'' without its shell

References

External links

Marine Species Identification Portal: ''Argonauta argo''

Tree of Life web project: ''Argonauta''
{{taxonbar, from=Q39514 argo Molluscs described in 1758 Taxa named by Carl Linnaeus