Talk about inconvenient, this week a nocturnal stalker has been creeping round my bathroom. The identity of this creeper, well its name is the Speckled Bush Cricket (Leptophyes punctatissima) and despite my best efforts the biting fiend doesn’t seem to want to be rescued. Last week’s animal, the giant Mydas Fly showed everyone the wonders of Batsien mimicry. This week we have a floating oceanic wanderer bobbing onto the scene, hope you guys enjoy.

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Issue #132 – Greater Argonaut

Kingdom – Animalia

Phylum – Mollusca

Class – Chephalopoda

Order – Octopoda

Family – Argonautidae

Genus – Argonauta

Species – argo

Related Species – The Greater Argonaut is one of the three species found in the genus Argonauta (1)

Range – The Greater Argonaut is found in tropical and sub-tropical waters around the world

Riding on the Waves

The Greater Argonaut is a floating species of pelagic octopus with the female reaching a maximum length of 30cm, while the male remains in a larval state rarely reaching a length of more than a few centimetres in length. Only the female creates the paper thin shell formed, not of Argonite like other mollusc species, but of a Calcite/Magnesium Carbonate composite. The thinness of the shell is what has earned the species the alternate name Paper Nautilus, despite the species not being closely related to the more well-known Nautilus (Nautilus sp). Like true Nautilus species however, the shell does control the Argonaut’s buoyancy using a bubble of air stored at the top of the structure (2).

Like all cephalopods, the Greater Argonaut is an obligate carnivore, with the majority of the feeding taking place during the day. Using its tentacles the Argonaut will grab a prey item, usually another floating invertebrate such as a sea slug or jellyfish and inject a toxic saliva into its victim to stun it and speed up digestion. Like all octopuses, the Greater Argonaut has numerous defensive tricks up its arsenal such as spraying ink and changing colour. Despite these defences, the partially digested shells of Argonauts are still occasionally found in the stomachs of pelagic fish such as tuna and marlin, as well as dolphins.

Argonaut mating involves the tiny male snapping off a specialised tentacle known as the hetrocotylus and passing it and the packages of sperm connected to the arm over to the female. From there the female will fertilise the eggs, carried in the lower section of the shell and then, once they hatch expel them out through the siphon into the open ocean (3). Unlike many cephalopods the Argonaut is able to breed multiple times, partially due to the portable nature of her eggs, thus negating the usual sacrifice female octopuses perform to ensure their eggs remain healthy until they hatch.

Five Fun Greater Argonaut Facts

The name Argonaut comes from the fusion of two Greek words Argo and nautilos, with the later word translating to sailor in English.

The whole belief about the Argonaut being able to sail comes from the misguided identification of the webbing found between the animals tentacles.

The misidentification continued up until the early 19^th century, with scientists believing the Argonaut used the discarded shells of other molluscs (much like a hermit crab) rather than create its own. The theory was eventually disproved by the pioneering French marine biologist Jeanne Villepreux-Power (4).

This wouldn’t be the last taxonomic tangle the Argonaut would face. Famous palaeontologist Georges Curvier incorrectly identified the appearance of the male hetrocotylus in the shell of female Argonauts as a species of parasitic worm.

Argonaut’s have been recorded hanging onto oceanic flotsam with their tentacles. Since the animal doesn’t naturally float, this could be a way to remain near the surface of the ocean when travelling long distances.

Bibliography

1 - www.arkive.org

2 - 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

3 - http://www.thecephalopodpage.org/MarineInvertebrateZoology/Argonautaargo.html

4 - Swaby, Rachel (2015). Headstrong: 52 Women Who Changed Science - And the World. New York: Broadway Books. pp. 51–53

Picture References

1 - http://www.seabean.com/thingsthatfloat/papernautilus/jpg/paper_nautilus.jpg

2 - https://qmtalksscience.files.wordpress.com/2011/09/argonaut.jpg

3 - https://curiouscox.files.wordpress.com/2011/12/argo.png

4 -http://67.media.tumblr.com/e660278f4c72265168ee9363df91f1ef/tumblr_inline_n2plfhQRLj1riz1wu.jpg

Hmm, well hopefully this issue will sail off into IGTA history as…well something. Next week we have a rapacious request from @cbishop, but until then make sure to critic, comment and suggest future issues as well as making sure you check past issues in Impurest’s Bestiary.

Many Thanks

Impurest Cheese

Want more IGTA? For another mollusc that drifts along with the current click here to meet the Sea Swallow. Or for another graceful cephalopod click here to meet the beautiful Blanket Octopus