Scientists finally discover how the female argonaut really uses its shell
The delicate shell of the argonaut, also known as the ‘paper nautilus’, has long featured in art, architecture, pottery and jewellery. Finding them washed up on the shore, sometimes with the octopus-like resident still inside, people since the ancient Greeks have speculated about what the shell might be for.
Aristotle proposed that the shell functioned as a boat, allowing the argonaut to sail on the water surface. ‘Argonaut’ means sailor (Greek ‘nautilus’, ναυτίλος) on the Argo (the ship of Greek mythology). The idea that argonauts raise their flanged dorsal tentacles as sails to catch the wind was widely accepted for over 2,000 years. But no-one ever observed them doing it.
Another wrong idea believed by many was that argonauts found inside shells washed up on beaches had stolen the shell from some other creature.
Note that only female argonauts were found in shells. It wasn’t until the late 19th century that male argonauts were discovered and described. The argonaut sexes are very different, displaying what biologists refer to as ‘extreme sexual dimorphism’.
Lacking a shell, males are only about as big as the eye of a female, and one six-hundredth of their body weight. Only the females have the distinctive pair of dorsal arms1 with web flanges. The webs secrete the mineral calcite (a form of calcium carbonate) to produce the shell, from very early in life, when the female’s mantle (i.e. the main part of her body behind the head) is only 7 mm long. As she grows bigger (up to 40 cm long), so her calcite-secreting webs enlarge the shell (up to 50 cm across).
The shell is now also known as an ‘eggcase’, where the female argonaut lays her eggs, protecting them there until they hatch.
Air in the shell: a calamity, or by design?
During the past 200 years, scientists debated whether air getting into the argonaut shell was beneficial or detrimental to survival. In various parts of the world, e.g. Japan, southern Australia, and the American west coast, argonauts are periodically found beached in large numbers after storms. The dominant theory was that air got caught in the shells when the argonauts went close to the sea surface, trapping them up there, then winds and waves would cast them ashore.
Biologists had certainly observed pockets of air trapped in the apex of female argonaut shells, especially in captivity. Aquarium-kept argonauts were reportedly often found ‘stranded’ at the water surface, because of air trapped in their shell.
However, researchers Drs Julian Finn and Mark Norman, from Museum Victoria (Melbourne, Australia), have recently shown not only that the female argonaut deliberately puts the air in her shell, and how she uses her shell to do it, but they also note a very important purpose for doing so.2,3
Diving with the argonauts
Armed with scuba gear and underwater video equipment and going down as far as seven metres below the sea surface, Finn and Norman manipulated captured argonauts so as to completely expel air from their shells, then released them.
It was soon obvious that air-less argonauts were ‘negatively buoyant’, i.e. they would have sunk but for the action of their jets propelling them upward. Also, they “appeared to have difficulty in maintaining the vertical orientation of the shell, which flailed from side-to-side as the animal jetted.”3
But not for long. In every case the argonauts …
- Immediately jetted up to the sea surface, then …
- Aimed their funnel backwards while jetting so as to cause the shell to bob above the water and rock forward, ‘gulping’ the maximum possible volume of air into the shell and sealing it off using the second pair of arms, then …
- Aimed the funnel jet forwards, causing the shell to roll away from the water surface, and …
- Forcibly jetted the now-buoyant shell downwards, until …
- They levelled out at the depth where buoyancy from the trapped (and now compressed) air volume counter-balanced their own weight, and they jetted away.
As Julian Finn further explained in a video, achieving ‘neutral buoyancy’ is of critical importance to the argonauts’ free-swimming existence in the ‘water column’:
“A problem that all animals have that live in open ocean, that live away from the sea floor up in the water column, is that they need to maintain their position. For the female argonaut the way that we found that she is attaining neutral buoyancy is that she’s going up and gathering air. And the air is extremely buoyant—it’s a large volume, but as you push the air down, the pressure of the water shrinks that air, and it becomes more compressed, and the buoyancy changes. And she pushes the air down to the point where the buoyant, the flotation nature of the air, and her weight, cancel out, so that she becomes neutrally buoyant, she becomes perfectly balanced between the upward pull and the downward pull, and then she’s able to swim effortlessly.”4
Indeed, as the researchers ruefully pointed out in their paper, “Once neutrally buoyant, the argonaut was capable of rapid swimming parallel to the water surface, at a speed that exceeded that of a swimming diver.”3
By design, not evolution
Finn and Norman write presuming an evolutionary framework, e.g.: “Evolution of this air-capture strategy enables this negatively buoyant octopus to survive free of the sea floor.”3 But is it reasonable to credit evolution with having conferred a ‘strategy’ that in the researchers’ own words is “a complex, multi-phase behavioural sequence”?3 And it is highly finessed, e.g. during the argonauts’ jetted descent from the sea surface the creatures changed the orientation of their shells as depth increased.
In shallower waters (2–3 m) the shell was held vertically and away from the body so that the larger volume of air could not escape. When descending to greater depths (7–8 m),5 the argonaut gradually rotated the shell towards horizontal and settled further into the shell as the air was compressed into the top of the shell by the increasing pressure.
Note also that by actively rocking the shell at the surface to capture air, the female can capture a larger volume of air than would be possible with a merely passive shell at the surface. This larger volume of air enables argonauts to maximize the depth at which they attain neutral buoyancy.
Where an argonaut cannot dive to sufficient depth—e.g. a shallow aquarium in a research laboratory—the large air volume within the shell draws the animal back to the water surface. But in normal circumstances, argonauts are master swimmers in their domain, with their shell functioning as “a hydrostatic structure … to precisely control buoyancy at varying depths”.3 As Julian Finn mused:
“I’ve studied argonauts for many years, and I’ve looked at thousands of shells in museums, and I’ve gone through old texts, and read up on the old writings. But it wasn’t until I actually got an argonaut in the water that I really saw the true marvel of these animals. I mean, this female argonaut knows exactly what she is doing. We as scientists thought, ‘Oh, the poor argonaut is getting air caught in its shell, or it doesn’t know how to get rid of it.’ Underwater, she was completely in control. She went straight to the surface, got the air she wanted, and swam out of sight.”4
Surely, she was designed to do what she does do, and what she does do, she does do well! In contrast, an evolutionary story of argonaut origins is up against formidable challenges. E.g. as Finn and Norman themselves point out, the mooted bottom-dwelling octopus/cephalopod ancestor of argonauts cannot have initiated the ‘air-gulping’ shell buoyancy control strategy at depth as the critical air is obtained from the sea surface.3 And what of the nautiloid ‘lookalikes’ (see Nautiloid lookalikes), distinctly different yet sharing some common design principles?—a common designer makes much more sense than evolutionary claims of ‘common ancestry’ and/or ‘convergent evolution’.6
Also, evolutionists must face the challenge of the argonauts’ unique mode of reproduction. The minute male’s 3rd left arm, called a ‘hectocotylus’, carries spermatophores7 to the female argonaut in the most incredible fashion.
When the hectocotylus explosively bursts out of a pouch just below the male’s eye, the male dies, but his hectocotylus ‘lives’ on,8 swimming to the female and attaching itself by means of suckers, then entering her mantle. It remains there until the female is ready to use it for fertilization. She can actually store several males’ hectocotyluses simultaneously, in advance of laying her eggs. In the early 19th century the zoologist Georges Cuvier discovered these in female argonauts and mistakenly thought they must be a type of parasitic worm, naming them after their ‘hundred suckers’, Hectocotylus octopodis.
Possibly evolutionists will come up with a believable-sounding story about the origins of argonaut reproduction,9 at least as creative and intelligently conceived as the notions that argonauts parasitize other creatures’ shells, hoist their flanged tentacles as sails, and suffer from air trapped in the shells and from hundred-sucker parasitic worms. The basic problem with all such stories is that they were expounded from incomplete eyewitness evidence or none at all (cf. Deuteronomy 19:15, 2 Corinthians 13:1). In contrast, the Bible’s reliable eyewitness account of key events in history leaves no room for evolution—rather, the seas teeming with life, filled from ocean surface to seabed with diverse kinds of sea creatures all reproducing according to their kinds, were created by God Almighty as His Word states (Genesis 1:20–21).
References and notes
- Argonauts and other creatures in the order Octopoda have eight arms—as four pairs labelled as dorsal, dorsolateral, ventrolateral, ventral. Return to text.
- Pidcock, R., Ancient octopus mystery resolved, bbc.co.uk, 19 May 2010. Return to text.
- Finn, J. and Norman, M., The argonaut shell: gas-mediated buoyancy control in a pelagic octopus, Proc. Roy. Soc. B. 277(1696):2967–2971, 2010. Return to text.
- Julian Finn speaking on the video: Julian Finn, Mark Norman, with Yasushi Okamura—Japan Underwater Films, youtu.be/EgISnrhSAmQ, acc. 11 August 2015. Return to text.
- From other observations of argonauts in the wild it seems 7–8 metres is generally their preferred target depth—possibly because it’s deep enough to escape surface wave action, and predation from above (i.e. from diving birds). Return to text.
- ‘Convergent evolution’ is the notion that similar biological features evolved independently multiple times across diverse classes of organisms. What faith is this, believing that complex design attributes could have evolved not just once but twice or even more times?! See: Batten, D., Are look-alikes related? Creation 19(2):39–41, 1997; creation.com/lookalikes. Return to text.
- Capsules containing the male’s sperm. Return to text.
- ‘Lives’? Evolutionist author Menno Schilthuizen wrote: “In one special group of cephalopods called argonauts, the hectocotylus even takes on a life of its own.” Schilthuizen, M., Nature’s nether regions: What the sex lives of bugs, birds, and beasts tell us about evolution, biodiversity, and ourselves, Chapter 1—Story 1, Penguin Books, New York, USA, 2014. Return to text.
- However, it’s probably not very likely, given evolutionists’ admissions that even in creatures with more ‘orthodox’ reproduction than that which the sexually dimorphic argonauts display, “How sex began and why it thrived remain a mystery.”—Wuethrich, B., Why sex? Putting the theory to the test, Science 281: 1980–1982, 1998. Similarly, atheist Richard Dawkins admitted: “To say, as I have, that good genes can benefit from the existence of sex whereas bad genes can benefit from its absence, is not the same thing as explaining why sex is there at all. There are many theories of why sex exists, and none of them is knock-down convincing.”—Dawkins, R., Climbing Mt Improbable, p.75, Penguin Books Ltd., Harmondsworth, Middlesex, England, 1997. Return to text.