Marine Invertebrates of Bermuda Paper Nautilus (Argonauta argo) By Marcie Orenstein and James B. Wood (Ed) Abstract Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links

Abstract


Argonauta argo is a species of octopus. Members of family Argonautidae are known for their acute sexual dimorphism, females with webbed dorsal arms capable of secreting calcareous egg cases, and dwarf males with hectocotylized third arms used for fertilization. A. argo resides in epipelagic tropical and subtropical waters and can utilize jetting, thigmotactic means, or possibly air bubbles within egg cases to remain buoyant. These animals often form associations with gelatinous marine species, utilizing them for food, locomotion, and protection. Like other octopuses, defense strategies of A. argo include camouflage and inking. Mating differs from most other octopuses in that A. argo females continue to grow and reproduce after spawning while males die after the loss of their third arm. Females can be fertilized by more than one hectocotylus over successive days by storing them in her mantle cavity. This results in eggs of multiple developmental stages within a single egg case. Egg cases sometimes wash ashore in mass strandings along coastlines, yet live argonauts are rather illusive. Lack of frequent contact with A. argo has resulted in a scarcity of information on the species.

Taxonomy


Phylum: Mollusca
  Class: Cephalopoda
    Order: Octopoda
      Family: Argonautidae


Habitat


A. argo begins life a planktonic larva in a narrow range of temperatures (18.5°C to 22.3ºC) but occupies a large range of salinities. Argonauts are the only octopuses that can also be found in the plankton as mature adults (Vecchione et al., 2001). There are only marine and estuarine argonauts and no freshwater species (Norman, 2003). A. argo is a cosmopolitan species found in all tropical and subtropical oceans and is often found in the epipelagic (<100m in depth)(Iliffe, 1982). Argonauts tend to accumulate near shores off island arcs due to winds, and some have even stranded on Bermudian beaches (Nesis, 1977; Iliffe, 1982).

Ecology


Synapomorphies

Argonauts, as a group of cephalopods, are defined as a taxon by distal webs on their first pair of arms able to secrete a calcium carbonate egg case. In general, argonauts share a number of features including an open ocean lifestyle, muscular bodies, a lack of fins, eight arms with two rows of suckers each, and dwarf males. The family Argonautidae is defined by females able to secrete egg cases from webbed appendages (Norman, 2003).

Morphology

The morphology of the argonaut egg case is commonly used to distinguish between species. The egg case, secreted by a female A. argo, consists of a narrow keel with two rows of sharp bumps, or tubercles, along its length. This laterally compressed, calcareous structure increases in thickness, forming a horn (Norman, 2003). Female egg cases tend to be longer than female mantle lengths, so individuals can often recede completely inside the structure (Commonwealth of Australia, 2001).

The first dorsal arms of female argonauts are webbed and are responsible for the secretion of the egg case. Females often travel with these webs sprawled across the lateral sides of their egg cases. The webs contain chromatophores able to change color from reflective silver to dark maroon (Normam, 2003).

A. argo is the largest of the argonaut species. Male argonauts tend to grow to about ten percent of the size of their female counterparts (Mangold et al., 1996; Young, 1998). This sexual dimorphism is readily apparent as males can only reach a maximum of several centimeters in length while females can be two meters long (Norman, 2003).

Buoyancy

As long ago as 300BCE, argonauts had been spotted by seegoers. Aristotle described the argonaut as sailing with its webbed dorsal arms protruding from the water to catch wind while using its egg case as a boat (Norman, 2007). It is now known, based on rare sitings, that argonauts do not, in fact, employ this buoyancy mechanism, although egg case ridges and webbed arms may aid in floatation (Norman, 2003). Manipulation of buoyancy may be controlled by air bubbles found in captured egg cases. These bubbles can be removed when the argonaut rotates its body, yet this mechanism has never been observed in action (Nesis, 1977).

A method of floatation that has been observed in argonauts is a tendency toward sticking to floating matter. This thigmotactic propensity could be an adaptation allowing the organism to drift passively in surface waters at night to lay eggs and release larvae (Nesis, 1977). Argonauts have been observed adhering to jellyfish, stomatopod larvae, pteropod shells, plant debris, pumice, objects two millimeters in diameter, and even each other at all developmental stages. Sometimes chains of 20 to 30 argonauts of comparable size can be seen floating on their sides in the open ocean (Saul and Stadium, 2005).

Association with Salps

One example of the argonaut’s thigmotactic tendencies is its association with salps. In the Gulf of Mexico, argonauts were observed residing within the branchial cavities of salps, their tentacles attached to the walls of the pharynx. The colonial salps harboring the juvenile argonauts were comprised of 40 to 60 individuals, and one male and one female argonaut were collected from separate salp chains. In addition to argonauts, the salps contained amphipods, copepods, and fish. After capture, the argonauts left their hosts, and no morphological damage to the salps was observed. It is believed that the association between salps and argonauts may allow argonauts to obtain food such as commensal amphipods, a means of floatation, and possibly camouflage. Protection is probably not a factor in the argonaut’s choice of host since perturbations via capture induced a fleeing response (Banas et al., 1982).

Association with Jellyfish

Salps are not the only gelatinous organisms with which argonauts associate. In the Phillipine archipelago, argonauts have been observed atop scyphomedusans with lateral and ventral arms gripping the exumbrella tightly. Aboral surfaces of these jellyfish are extremely damaged, and large pieces of mesoglea were missing. Two holes (20 by 10mm and 5 by 2mm) are believed to be bite marks from horny mandables. Blue perimeters were noted near the surface of the bell. Five channels lead from these bite marks through the mesoglea to the gastral cavity, probably to extract food. In addition to food, the medusa-argonaut association could provide shelter, camouflage, or protection to the argonaut since argonaut predators like tunas, dolphinfishes, and swordfishes usually avoid scyphozoans as prey (Heeger et al., 1992).

Nematocysts are used to ward off potential predators of jellyfish, but interesting results were obtained in experiments on scyphomedusan contact with cuttlefish and catfish. When attached to jellyfish, the number of penetrated nematorcysts on the surfaces of these two animals was counted. Fewer nematocysts discharged on the mantles of the cuttlefish than the surfaces of the catfishes, perhaps because cuttlefish mantles do not carry substances prone to trigger nematocyst release. These results might be extrapolated to other cephalopods, such as argonauts(Heeger et al., 1992).

Prey/Predators/Defense

Cephalopods like A. argo are top level predators that usually feed on sea butterflies (planktonic pteropod mollusks) and small fishes, as well as the occasional octopod (Iliffe, 1982). Shrimp are also consumed by captive argonauts but only when placed directly into the beak or when touched to webbing on female dorsal arms. Unlike other cephalopods, reproduction does not inhibit feeding. When stomachs of 52 captured argonauts were analyzed, 90% of them were found to be empty, indicating a rapid digestion rate (Nesis, 1977).

Predators of argonauts include yellowfins, bigeye tunas, seabirds, and lancelets that feed at depths of 100 to 300m, indicating argonauts do not always reside in the surface layer of the epipelagic zone (Nesis, 1977; Norman, 2003). To avoid these predators, argonauts have developed defense strategies like inking and countershading. Argonauts can shoot a minimum of five shots of dark gray, viscous ink that hangs in the water and slowly elongates. This pseudomorph disorients predators while the argonaut quickly escapes via jet propulsion (Nesis, 1977). Countershading in argonauts is also an effective predator avoidance tactic. Argonauts are darker on their dorsal surface and reflective silver on their ventral surface, an important trait for these near-surface dwellers (Iliffe, 1982).

Mass Strandings

Observations of A. argo are usually in the form of mass strandings and mass mortalities along coastlines. These strandings have been known to occur in Japan, Australia, and California (Norman, 2003; Saul and Stadium, 2005). Sometimes over 1000 egg cases at a time can be brought ashore by weather or currents, and in the case of California, red tides that reduce oxygen in surface waters could have been responsible for argonaut mass mortalities (Norman, 2003; Saul and Stadium, 2005).

Mating

Although live male argonauts have never been observed in the wild, a basic understanding of fertilization in argonauts has been attained based on dead male and living female specimens (Norman, 2003). The male argonaut has a modified third left arm that carries and stores sperm. This arm develops in a pouch under the male’s eye until needed for fertilization, at which point it explodes out of its sheath and leaves the body (Nesis, 1977; Iliffe, 1982). The arm attaches to the outside of the female’s mantle via suckers, then autonomously wiggles into the mantle cavity (Nesis, 1977). Originally, this arm was thought to be a parasitic worm andwas given the scientific name Hectocotylus, and the modified arm is still called a hectocotylis in octopuses and squids. The detached arm is free-swimming and very active, but it probably cannot seek out females since it lacks a sense of direction (Iliffe, 1982). Upon expulsion of the hectocotylus, the male dies, and the arm, with its threadlike organ to carry and store spermatophores, remains in the female’s mantle cavity until such time as she chooses to fertilize it (Iliffe, 1982; Norman, 2003).

Female argonauts can have a few hectocotyluses within their mantle cavities simultaneously and often lay eggs after attaining spermatophores (Norman, 2003). The female attaches strings of eggs to her egg case that is created when the female’s mantle reaches 6.5 to 7mm in length, and protects them as they develop (Commonwealth of Australia, 2001; Norman, 2003). Egg clusters are connected by a stalk and attached to the apex of the egg case with the earliest larval developmental stages closest to the top (Commonweath of Australia, 2001).

Reproduction

Female argonauts typically lay eggs successively over a period of three nights. The most developed eggs in the egg case react to irritation with chromatophore displays and release ink within the confines of their eggs. Argonauts release larvae at night like other benthic octopuses (Nesis, 1977). The female can draw the hatchlings into her gill cavity and squirt up to 100 at a time away from herself (Norman, 2003). Planktonic larvae tend to “hop” around moving five to ten millimeters at a time. Unlike most other cephalopods, female argonauts live to grow and reproduce again after spawning (Nesis, 1977).

It was recently found that reproductive strategies of A. argo and other argonaut species in the Aegean Sea lay significantly larger eggs than conspecifics in the western Mediterranean and open ocean. Low potential batch fecundity was found in the Aegean. It is hypothesized that argonauts in the Aegean Sea changed to a more K-select strategy because the environment is more stable than the open ocean (Laptikhovsky and Salman, 2003).

Recent Research


Recently, scientists have examined fossilized argonaut egg cases found in late Miocene siltstones in Los Angeles. These are the first fossilized argonauts to be reported in the western hemisphere. Scientists believe argonauts probably started secreting egg cases during the Paleogene in response to their spawning practices in the epipelagic zone. Egg cases may have protected larvae from UV radiation (Saul and Stadium, 2005).

Another recent endeavor undertaken on A. argo specimens is the utilization of paper nautilius skin as a collagen source. Collagen is a protein abundant in the body and current sources include pig and cow skin and bones. A large quantity of collagen was able to be extracted from the outer skin of paper nautiluses that could be used in place of mammalian collagen in cosmetics, biomedical materials, and food (Nagai and Suzuki, 2002).

Commercial Importance


It is estimated that more than three million tons of cephalopods are caught annually constituting more than six billion dollars in revenue. This number may be an underestimate because commercial catches are not always reported (Norman, 2003). Part of these catches comes from trawlers in Italian and Spanish Mediterranean ports. In these locals, cephalopods seem to be commercially important in shallower waters constituting 8.2 to 30% of commercially retained catches. Cephalopods as food sources might be so important in Mediterranean countries because they have been caught commercially there since ancient times, engraining them in the culture. However, A. argo isn't a targeted food species. Most of the cephalopods caught in these trawlers are octopuses, cuttlefish, and squid (Sartor et al., 1998). Cephalopods are also commercially important for native Filipinos who often use washed up A. argo egg cases in shell crafts (Heeger et al., 1992)

Bermuda Laws


There are currently no Bermuda laws directly pertaining to A. argo. In 1986, however, Bermuda established 29 marine protected areas in which no fishing or collection could occur. Currently, there are 19 such sites. Should A. argo be spotted in these areas, it could not be collected (de Putron, 2007).

Personal Interest


In college, after taking an animal diversity course, I became interested in marine invertebrates, especially those in phyla Mollusca, Ctenophora, and Cnidaria. Since I had already completed a research project on ctenophores in the aforementioned course, and cnidarians are very similar to ctenophores, I decided to pick a species of mollusk for this project. Nudibranchs have always fascinated me, but knowing a fair deal about them already, I decided to choose a more obscure species. The idea of an octopus secreting a shell-like egg case and the illusive nature of A. argo attracted me to the topic.

References

Banas P.T., Smith D.E. Biggs D.C. (1982). An association between a pelagic octopod, Argonauta sp. Linnaeus 1758, and aggregate salps. Fish. Bull. U.S. 80: 648-650.

Commonwealth of Australia (2001). Zoological Catalogue of Australia 17.2, pp. 146-149. Australia: CSIRO PUBLISHING.

de Putron S. “Human impacts on the sea.” Bermuda Institute of Ocean Sciences. Ferry Reach Bermuda. 1 March, 2007.

Heeger T., Piatkowski U., Moller H. (1992). Predation on jellyfish by the cephalopod Argonauta argo. Mar. Ecol. Prog. Ser. 88: 293-296.

Iliffe T.M. (1982). Argonaut: octopus in a parchment shell. Sea Frontiers. 28: 224-228.

Laptikhovsky V. and Salman A. (2003). On reproductive strategies of the epipelagic octopods of the superfamily Argonautoidea (Cephalopoda: Octopoda). Marine Biology. 142: 321-326.

Mangold (1922-2003), Katharina M., Vecchione, Michael, and Young, Richard E. 1996. Argonautidae Tryon, 1879. Argonauta Linnaeus 1758. paper nautilus. Version 01 January 1996 (under construction). http://tolweb.org/Argonauta/20204/1996.01.01 in The Tree of Life Web Project, http://tolweb.org/

Nagai T. and Suzuki N. (2002). Preparation and partial characterization of collagen from paper nautilus (Argonauta argo, Linnaeus) outer skin. Food Chemistry. 76: 149-153.

Nesis K.N. (1977). The biology of paper nautiluses, Argonauta boettgeri and Argonauta hians (cephalopods, octopoda) in the western Pacific Ocean and the seas of the East Indian archipelago. Zoologichesky Zhurnal. 56: 1004-1014.

Norman, M. (2003). Cephalopods: A World Guide, pp.189-197. Germany: ConchBooks.

Norman, M. (2007). http://researchdata.museum.vic.gov.au/argosearch/index.html

Sartor P., Belcari P., Carbonell A., Gonzales M., Quetglas A., Samchez P. (1998). The importance of cephalopods to trawl fisheries in the western Mediterranean. S. Afr. J. mar. Sci. 20: 67-72.

Saul L.R. and Stadium C.J. (2005) Fossil argonauts (mollusca: cephalopoda: octopodida) from late Miocene siltstones of the Los Angeles basin, California. J. Paleont. 79: 520-531.

Vecchione M., Sweeney M.J., Roper C.F.E., Lu C.C. (2001). Distribution, relative abundance and developmental morphology of paralarval cephalopods in the western North Atlantic Ocean. NMFS Technical Reports. 40-43.

Young R.E., Vecchione M., Donovan D. (1998) The evolution of coleoid cephalopods and their present biogiversity and ecology. South African Jour. Mar. Sci. 20: 393-420.

Links

ArgoSearch Sciences Museum Victoria
Tree of Life Web Project
University of Michigan Museum of Zoology Animal Diversity Web
The Cephalopod Page
CephBase