Overview
Brief Summary
Introduction
Argonauts are muscular, pelagic octopods. Females secrete a thin calcareous "shell" in which they reside. Shells may reach a length of 30 cm (Nesis, 1982). The dorsal arms of females are modified with large, flag-like membranes that expand over the shell and are responsible for the secretion of the shell. Eyes are very large and webs very small. The mantle-funnel locking apparatus consists of knob-like cartilages (mantle) and matching depressions (funnel). Males are dwarfs.
Brief diagnosis:
An argonautoid ...
- with distal webs on arms I in females that secrete a calcareous shell.
- with a circular pit in the funnel locking-apparatus.
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Comprehensive Description
Origin of the Argonaut Shell
An unusual feature of argonauts is the secreted shell that functions as a brood chamber. The "shell" is not homologous with the true molluscan shell as evidenced by its unique site of formation: the dorsal arms of the female rather than the internal shell sac as in other coleoids. Naef (1921/3) noted the remarkable resemblance of the argonaut shell to the shells of some of the abundant Cretaceous ammonoids and suggested that the argonaut shell evolved in the following way: Ancestral argonauts occupied empty ammonoid shells during the late Cretaceous. [Occupancy of molluscan shells by octopodids is common in the present day.] The octopod evolved glandular structures on the arms to repair the shell of the ammonoids after the latter had become extinct at the end of the Cretaceous. Eventually, the ammonoid shell was completely replaced by a secreted structure whose shape had been evolutionarily molded by the ammonoid shell. However, as pointed out by Young et al. (1998), a gap of about 40 million years exists between extinction of ammonoids and the earliest fossil record of an argonaut, and they suggest that the mold for the shell was from some other type of mollusc and that the resemblance to ammonoids is coincidental. The origin of the argonaut shell is a challenging problem and has important implications for understanding the relationships amoung groups of the Argonautoidea (Young, et al., 1998).
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Nomenclature
A list of all nominal genera and species in the Argonautidae can be found here. The list includes the current status and type species of all genera, and the current status, type repository and type locality of all species and all pertinent references.
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Characteristics
- Arms
- Females with distal flag-like expansion of the web of the dorsal arms that contain shell-secreting glands.
Figure. Lateral view of a juvenile female (6.5 mm ML) Argonauta hians showing the web on arms I, equatorial South Atlantic. Drawing from Chun, 1910.
- Presence of external "shell" in females secreted by the dorsal arms. The true molluscan shell (i. e., stylets in most incirrates) is absent.
Figure. Side view of Argonauta sp., showing the expansion of the web (web presence indicated by their chromatophores) of the first arm, past the horn of the shell and over most of the shell surface, Gulf of Aqaba, Red Sea. Photograph of living argonaut by Shai Enbinder; provided by Nadav Shashar.
Figure. Side-oblique views of an Argonauta argo, photographed in a ship-board aquarium. Left - Arm I web expanded over shell. Right - Arm I web retracted. Photographs by M. Vecchione.
- Females with distal flag-like expansion of the web of the dorsal arms that contain shell-secreting glands.
- Head
- Beaks: Descriptions can be found here: Lower beak; upper beak.
- Water pores: Water pores absent.
- Radula: First lateral tooth of radula not greatly reduced in size.
- Beaks: Descriptions can be found here: Lower beak; upper beak.
- Sexual dimorphism
- Males dwarf.
- Males dwarf.
- Funnel
- Funnel-mantle locking apparatus consists of a knob and pit.
Figure. Side and ventral views of the funnel and mantle locking-apparatus of Argonauta hians, juvenile male, 5.0 mm ML, equatorial South Atlantic. Drawing from Chun, 1910.
- Funnel-mantle locking apparatus consists of a knob and pit.
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Ecology
Habitat
Water temperature and chemistry ranges based on 84 samples.
Environmental ranges
Depth range (m): 0 - 4935
Temperature range (°C): 2.203 - 27.746
Nitrate (umol/L): 0.065 - 41.060
Salinity (PPS): 34.066 - 39.011
Oxygen (ml/l): 1.758 - 6.187
Phosphate (umol/l): 0.027 - 2.909
Silicate (umol/l): 0.801 - 132.094
Graphical representation
Depth range (m): 0 - 4935
Temperature range (°C): 2.203 - 27.746
Nitrate (umol/L): 0.065 - 41.060
Salinity (PPS): 34.066 - 39.011
Oxygen (ml/l): 1.758 - 6.187
Phosphate (umol/l): 0.027 - 2.909
Silicate (umol/l): 0.801 - 132.094
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
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Habitat
Argonauts are pelagic in tropical and subtropical surface waters of all oceans and seas. Sometimes they are found in large swarms, but only rarely are they encountered nearshore. In the open ocean they are commonly found attached to jellyfish (David, 1965). While this unusual association between Argonauta spp. and jellyfish has long been known (Kramp, 1956; David, 1965) it was uninvestigated prior to the work of Heeger et al. (1992). The latter authors describe Argonauta astride the aboral (=exumbrellar) surface of a swimming jellyfish that it held with its lateral and ventral arms. Upon examination of the jellyfish they found about half of its aboral surface was damaged and large pieces of mesoglea were missing. Two holes, apparently bite marks were found in the center of this area and channels led from these holes into the gastral cavity of the jellyfish. They presumed the octopod used these channels to suck particles (food) from the gastral cavity. They also suggest that the association provided shelter or camouflage for the argonaut.
Figure. Two views of Argonauta argo atop the jellyfish, Phyllorhiza punctata. Photographs Copyright ©, Thomas Heeger, University of San Carlos, Philippines.
Males have been reported living within salps (Banas et al., 1982).
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Life History and Behavior
Life Cycle
Life history
The male argonaut is a dwarf, about 10% of the length of the female. The entire third right arm is hectocotylized and carried in a special sac. At mating, the hectocotylus, which carries one large spermatophore, breaks out of its sac and then from the male body. The free hectocotylus invades, or is deposited in, the female's mantle cavity, where it remains viable and active for some time. The hectocotylus was first described as a worm parasitic on the female (Delle Chiaje, 1825).
Figures. Lateral and oral views of male argonauts. Left, center - A 5 mm ML, apparently immature, male Argonauta hians from the equatorial South Atlantic. Drawings from Chun, 1910. In oral view the male looks like a 7-arm octopus. Right - A male Argonauta nodosa, off Australia, with the hectocotylus in a much larger sac is apparently mature. Photograph by Mandy Reid; provided by Mark Norman.
The female lives in a thin, calcareous, laterally compressed shell secreted by its dorsal arms. The shell is paper-thin and the animal is commonly called the "paper nautilus." The latter part of the name comes from similarly-shaped shell of Nautilus. The shell of the pearly nautilus, however, is the true cephalopod shell (i.e., the homologue of the molluscan shell) and not a unique evolutionary innovation like the "shell" of Argonauta (Naef, 1921-23).
Figure. Left - Lateral view of an Argonauta argo shell, Hawaii. Photograph by R. Young). Right - A collection of Argonauta nodosa shells from a swarm that washed ashore, Australia. Photograph by Mark Norman.
Embryonic development begins in the oviducts. Older embryos are attached to the inner region of the shell where they are brooded. The elongate egg stalks (extensions of the egg chorion) are woven together and attached to the shell apex on its inner surface. A female A. argo with a shell length of 88 mm was estimated to be carrying 48,800 embryos (Okutani and Kawaguchi, 1983). The eggs are very small (0.6 - 1.0 mm). Spawning is intermittent, and the brooding embryos can be seen to be in different stages of development.
The argonaut paralarva has a distinctive appearance as seen in the photo. The arms are very short and equal in length and are surrounded in their proximal half by a membranous collar or cuff (barely recognizable in the photograph) formed by the interbrachial membrane. The latter feature is found also in Tremoctopus hatchlings. The life-span is unknown.
Figure. Ventrolateral view of Argonauta argo hatchling from a plankton tow, Hawaii. Note the lock and pit of the funnel/mantle locking-apparatus at the bottom of the photograph. Photograph by R. Young.
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Wikipedia
Argonaut (animal)
- For other uses, see Argonaut (disambiguation).
The argonauts (genus Argonauta, the only extant genus in the Argonautidae family) are a group of pelagic octopuses. They are also called paper nautiluses, referring to the paper-thin eggcase that females secrete. This structure lacks the gas-filled chambers present in chambered nautilus shells and is not a true cephalopod shell, but rather an evolutionary innovation unique to the genus Argonauta.[1] It is used as a brood chamber and for trapped surface air to maintain buoyancy.
Argonauts are found in tropical and subtropical waters worldwide; they live in the open ocean, i.e. they are pelagic. Like most octopuses, they have a rounded body, eight arms and no fins. However, unlike most octopuses, argonauts live close to the sea surface rather than on the seabed. Argonauta species are characterised by very large eyes and small distal webs. The funnel–mantle locking apparatus is a major diagnostic feature of this taxon. It consists of knob-like cartilages in the mantle and corresponding depressions in the funnel. Unlike the closely allied genera Ocythoe and Tremoctopus, Argonauta species lack water pores.
Of its names, "argonaut" means "sailor on the Argo"; "nautilus" is derived from the Greek ναυτίλος, meaning "sailor", because it was formerly supposed that Argonauta used their shell-secreting arms as sails when they were at the surface.
The chambered nautilus was later named after the argonaut, but belongs to a different order, the Nautilida.
Contents |
Physical description
Sexual dimorphism and reproduction
Argonauts exhibit extreme sexual dimorphism in size and lifespan. Females grow up to 10 cm and make shells up to 30 cm, while males rarely surpass 2 cm. The males only mate once in their short lifetime, whereas the females are iteroparous, capable of having offspring many times over the course of their lives. In addition, the females have been known since ancient times, while the males were only described in the late 19th century.
The males lack the dorsal tentacles used by the females to create their eggcases. The males use a modified arm, the hectocotylus, to transfer sperm to the female. For fertilization, the arm is inserted into the female's pallial cavity, then is detached from the male. The hectocotylus when found in females was originally described as a parasitic worm.[2]
Eggcase
Female argonauts produce a laterally-compressed calcareous eggcase in which they reside. This "shell" has a double keel fringed by two rows of alternating tubercles. The sides are ribbed with the centre either flat or having winged protrusions. The eggcase curiously resembles the shells of extinct ammonites. It is secreted by the tips of the female's two greatly expanded dorsal tentacles (third left arms) before egg laying. After she deposits her eggs in the floating eggcase, the female takes shelter in it, often retaining the male's detached hectocotylus. She is usually found with her head and tentacles protruding from the opening, but she retreats deeper inside if disturbed. These ornate curved white eggcases are occasionally found floating on the sea, sometimes with the female argonaut clinging to it. It is not made of aragonite as most other shells are, but of calcite, with a three-layered structure[3] and a higher proportion of magnesium carbonate (7%) than other cephalopod shells.[4]
The eggcase contains a bubble of air that the animal captures at the surface of the water and uses for buoyancy, in a manner similar to other shelled cephalopods, although it does not have a chambered phragmocone as do other shelled cephalopods.[3] Once thought to contribute to occasional mass strandings on beaches, the air bubble is under sophisticated control, evident from the behaviour of animals from which air has been removed under experimental diving conditions.[5][6][7]
Most other octopuses lay eggs in caves; Neale Monks and C. Phil Palmer speculate that, before ammonites died out during the Cretaceous–Paleogene extinction event, the argonauts may have evolved to use discarded ammonite shells for their egg laying, eventually becoming able to mend the shells and perhaps make their own shells.[8] However, this is uncertain and it is unknown whether this is the result of convergent evolution.
Argonauta argo is the largest species in the genus and also produces the largest eggcase, which may reach a length of 300 mm.[9][10] The smallest species is Argonauta bottgeri, with a maximum recorded size of 67 mm.[9][11]
Female A. nodosa with its eggcase
The eggcase of A. argo
The eggcase of A. nodosa
The eggcase of A. hians
Beak
The beaks of Argonauta species are distinctive, being characterised by a very small rostrum and a fold that runs to the lower edge or near the free corner. The rostrum is 'pinched in' at the sides, making it much narrower than in other octopuses, with the exception of the closely allied monotypic genera Ocythoe and Vitreledonella. The jaw angle is curved and indistinct. Beaks have a sharp shoulder, which may or may not have posterior and anterior parts at different slopes. The hood lacks a notch and is very broad, flat, and low. The hood to crest ratio (f/g) is approximately 2-2.4. The lateral wall of the beak has no notch near the wide crest. Argonaut beaks are most similar to those of Ocythoe tuberculata and Vitreledonella richardi, but differ in 'leaning back' to a greater degree than the former and having a more curved jaw angle than the latter.[11]
Feeding and defense
Feeding mostly occurs during the day. Argonauts use tentacles to grab prey and drag it toward the mouth. It then bites the prey to inject it with poison from the salivary gland. They feed on small crustaceans, molluscs, jellyfish and salps. If the prey is shelled, the argonaut uses its radula to drill into the organism, then inject the poison.
Argonauts are capable of altering their color. They can blend in with their surroundings to avoid predators. They also produce ink, which is ejected when the animal is being attacked. This ink paralyzes the olfaction of the attacker, providing time for the argonaut to escape. The female is also able to pull back the web covering of her shell, making a silvery flash, which may deter a predator from attacking.
Argonauts are preyed upon by tunas, billfishes, and dolphins. Shells and remains of argonauts have been recorded from the stomachs of Alepisaurus ferox and Coryphaena hippurus.[11]
Male argonauts have been observed residing inside salps, although little is known about this relationship.[12]
Classification
The genus Argonauta contains up to seven extant species. Several extinct species are also known.
†Argonauta absyrtus
Argonauta argo (type)
Argonauta bottgeri
Argonauta cornuta*
Argonauta hians
†Argonauta itoigawai
†Argonauta joanneus
Argonauta nodosa
Argonauta nouryi
Argonauta pacifica*
†Argonauta tokunagai
- *Species status questionable.
The extinct species Obinautilus awaensis was originally assigned to Argonauta, but has since been transferred to the genus Obinautilus.[13]
Dubious or uncertain taxa
The following taxa associated with the family Argonautidae are of uncertain taxonomic status:[14]
| Binomial name and author citation | Current systematic status | Type locality | Type repository |
|---|---|---|---|
| Argonauta arctica Fabricius, 1780 | Undetermined | Unresolved; ?Tullukaurfak, Greenland | Unresolved |
| Argonauta bibula Röding, 1798 | Undetermined | Unresolved | Unresolved |
| Argonauta compressa Blainville, 1826 | Undetermined | Mer de Indes | Unresolved; [other Blainville types at MNHN] [not reported by Lu et al. (1995)] |
| Argonauta conradi Parkinson, 1856 | Species of uncertain status [fide Robson (1932:200)] | "New Nantucket, Pacific Ocean" | Unresolved |
| Argonauta cornu Gmelin, 1791 | Undetermined | Unresolved | Unresolved; LS? |
| Argonauta cymbium Linné, 1758 | Non-cephalopod; foraminiferous shell [fide Von Martens (1867:103) | ||
| Argonauta fragilis Parkinson, 1856 | Species of uncertain status [fide Robson (1932:200)] | Not designated | Unresolved |
| Argonauta geniculata Gould, 1852 | Species of uncertain status [fide Robson (1932:200)] | Near Sugarloaf Mountain, Rio de Janeiro, Brazil | Type not extant [fide Johnson (1964:32)] |
| Argonauta maxima Dall, 1871 | Nomen nudum | ||
| Argonauta navicula Lightfoot, 1786 | Species dubium [fide Rehder (1967:11)] | Not designated | Unresolved |
| Argonauta rotunda Perry, 1811 | Non-cephalopod; Carcinaria sp. [fide Robson (1932:201)] | ||
| Argonauta rufa Owen, 1836 | Incertae sedis [fide Robson (1932:181)] | "Indian seas" ["South Pacific ocean" fide Owen (1842:114)] | Unresolved; Museum of the Royal College of Surgeons? Holotype |
| Argonauta sulcata Lamarck, 1801 | Nomen nudum | ||
| Argonauta tuberculata f. aurita Von Martens, 1867 | Undetermined | Unresolved | ZMB |
| Argonauta tuberculata f. mutica Von Martens, 1867 | Undetermined | Coast of Brazil | ZMB Holotype |
| Argonauta tuberculata f. obtusangula Von Martens, 1867 | Undetermined | Not designated | ZMB Syntypes |
| Argonauta vitreus Gmelin, 1791 | Undetermined | Not designated | Unresolved; LS? |
| Octopus (Ocythoe) raricyathus Blainville, 1826 | Undetermined [Argonauta?] | Not designated | MNHN Holotype; specimen not extant [fide Lu et al. (1995:323)] |
| Ocythoe punctata Say, 1819 | Argonauta sp. [fide Robson (1929d:215)] | Atlantic Ocean near the North American coast (from stomach of dolphin) | Unresolved; ANSP? Holotype [not traced by Spamer and Bogan (1992)] |
| Tremoctopus hirondellei Joubin, 1895 | Argonauta or Ocythoe [fide Thomas (1977:386)] | 44°28′56″N 46°48′15″W / 44.48222°N 46.80417°W (Atlantic Ocean) | MOM Holotype [station 151] [fide Belloc (1950:3)] |
In design
The argonaut was inspiration for a number of classical and modern art and decorative forms including use on pottery and architectural elements. Some early examples are found in Minoan art from Crete.[15] A variation known as the double argonaut design was also found in Minoan jewelry.[16]
In literature and etymology
- Argonauts are featured in Twenty Thousand Leagues Under the Sea, noted for their ability to use their tentacles as sails. There is no evidence for this.
- A female argonaut is also described in Marianne Moore's poem "The Paper Nautilus."
- "Argonauta" is the name of a chapter in Anne Morrow Lindbergh's Gift from the Sea.
- Paper nautiluses were caught in the The Swiss Family Robinson novel.[17]
- Argonauts gave their name to an Arabidopsis thaliana mutation and by extension to Argonaute proteins.
References
- ^ (German) Naef, A. (1923). "Die Cephalopoden, Systematik". Fauna Flora Golf. Napoli (35) 1: 1–863.
- ^ (Italian) Delle Chiaje, S. (1825). Memorie sulla storia e notomia degli animali. Senza Vertebre del Regno di Napoli. I.
- ^ a b Nixon, M. & J.Z. Young (2003). The Brains and Lives of Cephalopods. Oxford University Press.
- ^ Saul, L. & C. Stadum (2005). "Fossil Argonauts (Mollusca: Cephalopoda: Octopodida) From Late Miocene Siltstones Of The Los Angeles Basin, California". Journal of Paleontology 79 (3): 520–531. doi:10.1666/0022-3360(2005)079<0520:FAMCOF>2.0.CO;2. ISSN 0022-3360. http://apt.allenpress.com/aptonline/?request=get-abstract&issn=0022-3360&volume=079&issue=03&page=0520.
- ^ Finn, J.K. & M.D. Norman 2010. The argonaut shell: gas-mediated buoyancy control in a pelagic octopus. Proceedings of the Royal Society B: Biological Sciences, published online May 19, 2010. doi:10.1098/rspb.2010.0155
- ^ "Museum Victoria 'Argonaut buoyancy' video" museumvictoria.com.au. URL accessed on 19 May 2010.
- ^ Pidcock, R. 2010. Ancient octopus mystery resolved. BBC News, May 19, 2010.
- ^ Monks, N. & P. Palmer (2002). Ammonites. Smithsonian Institution Press, Washington D.C..
- ^ a b Pisor, D. L. (2005). Registry of World Record Size Shells (4th ed.). Snail's Pace Productions and ConchBooks. pp. 12.
- ^ (Russian) Nesis, K. N. 1982. Abridged key to the cephalopod mollusks of the world's ocean. Light and Food Industry Publishing House, Moscow, 385+ii pp. [Translated into English by B. S. Levitov, ed. by L. A. Burgess (1987), Cephalopods of the world. T. F. H. Publications, Neptune City, NJ, 351 pp.]
- ^ a b c Clarke, M. R. (1986). A Handbook for the Identification of Cephalopod Beaks. Oxford University Press. pp. 273 pp.
- ^ Banas, P. T., D. E. Smith & D. C. Biggs (1982). "An association between a pelagic octopod, Argonauta sp. Linnaeus 1758, and aggregate salps". Fish. Bull. U.S. 80: 648–650.
- ^ Martill, D.M. & M.J. Barker (2006). A paper nautilus (Octopoda, Argonauta) from the Miocene Pakhna Formation of Cyprus. Palaeontology 49 (5): 1035-1041.
- ^ Sweeney, M. J. Taxa Associated with the Family Argonautidae Tryon, 1879. Tree of Life web project.
- ^ Eleni M. Konstantinidi, Jewellery Revealed in the Burial Contexts of the Greek Bronze Age, 2001, Hadrian Books, 322 pages ISBN 1-84171-165-9
- ^ C.Michael Hogan, Knossos Fieldnotes, The Modern Antiquarian (2007)
- ^ Johann David Wyss and Jenny H. Stickney, The Swiss Family Robinson, Ginn & Co., 1898, 364 pages
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