Have you ever heard of an octopus hitchhiker going for a ride on a jellyfish? It’s wild but true! Danna Staaf, the author of Monarchs of the Sea, is here to share her knowledge of Argonauts and their method of transportation. Let’s give her a big howdy Octonation!
Suppose you’re a gelatinous marine creature like a jellyfish or a salp, drifting through the blue expanse of the open ocean. You pass blooms of red and green algae, schools of silvery fish, and the occasional sea turtle or whale.
Then you come across a small octopus.
It might have a little white shell, or one of its eight arms might be absurdly larger than the others. In either case, it reaches toward you, clearly seeking a ride…
What should you do?
The likely outcome of picking up an octopus hitchhiker depends on what kind of gelatinous animal you are.
If you’re a salp, a transparent barrel constantly filtering your planktonic meals from the surrounding water, then you may already live in a colony of dozens of identical barrels linked in a chain.
Not only are you attached to other members of your own species, but the spacious cavity inside your body often serves as a temporary home for small fish and shrimp.
Why not add an octopus?
Can an octopus really live inside a salp?
Yes! Scientists first described octopuses living inside salps in 1982. They theorized that the octopuses derive the same potential benefit as fish and shrimp squatters: transportation.
Salps are surprisingly efficient swimmers, using the power of jet propulsion to migrate thousands of feet up and down in the water each day.
Octopus hitchhikers may also gain protection from predators. Although a salp’s clear body provides no visual cover, it’s tough enough to obstruct physical access.
That is unless a predator is small enough to climb inside the salp. Like, for example, a little octopus. As carnivores that readily consume both shrimp and fish, octopuses may view a salp chain as a traveling buffet!
Argonauts: sailors with strange sexes
Of course, to even encounter salps, an octopus must belong to a pelagic, or open-ocean, species. The most common pelagic octopuses found inside salps are Argonauts, going back to the 1982 discovery of one male and one female, both juveniles.
Of all octopuses, argonauts have some of the most extreme sex differences!
Female argonauts grow to about the size of a human hand and create beautiful translucent shells, which they use to control their buoyancy and brood their eggs.
By contrast, no one had any idea what male argonauts looked like for hundreds of years–or if they even existed. At one point, “parasitic worms” inside the shells of mature females were proposed to be male argonauts.
Eventually, researchers figured out that these “worms” were actually the detached arms of dwarf males, who are no bigger than a penny. Each male grows one arm much larger than the other seven and keeps it tucked in a pouch until the time comes to mate.
Then, loaded with sperm, the oversized arm detaches from the rest of the male’s body and takes up residence in the female’s shell, where she will eventually use it to fertilize her eggs.
How tiny is a male argonaut?
Male argonauts are so tiny that even as adults they could fit inside a salp, but only juvenile females can squeeze inside one of these barrels.
However, females of nearly any size can ride on top of other gelatinous organisms.
And, if you happen to be a jellyfish who’s been hearing from salps that it’s no big deal to pick up an octopus passenger, you may want to think again.
An octopus hitchhiker… they really exist!
The first scientific study of an argonaut riding a jellyfish, published in 1992, revealed that the octopus’s use of its mount went well beyond transportation.
This poor creature, an Australian spotted jellyfish, had been pressed into service as both taxi and snack.
The argonaut rider, an adult female, had bitten two holes in the jellyfish’s bell, with channels leading from these holes to the jelly’s stomach. The study authors suggested that she’d been sucking food through these channels that the jelly had collected for itself.
Impressive. And ice-cold.
How big is a female argonaut?
Female argonauts can be as large as or even larger than the jellies to which they cling, and they’re perfectly capable of swimming on their own, which leads one to wonder at what point “hitching a jelly ride” becomes “kidnapping a jelly passenger.”
It’s probably a vague distinction.
Argonauts are clingy creatures with a tendency to grasp a wide variety of surfaces, from leaves that have fallen in the sea to each other’s shells.
A group of adult females will sometimes attach one to the next, creating a chain almost reminiscent of a salp colony–though, unlike salps, their bodies are not fused together, nor are they cloned siblings.
What goes together like octopus and jelly?
Argonauts are not the only pelagic octopuses to engage with jellies in creative ways–to do at least two of their close cousins, the Football Octopus and the Blanket Octopus. These species also have dwarf males with detachable arms and large females with unusual features.
Football Octopus vs Blanket Octopus- what’s the difference?
The Female Football Octopus is the only cephalopod with a gas bladder, while the female Blanket Octopus has enormous banner-like arm webs. Young Football Octopuses ride on jellyfish bells and inside salps, while juvenile Blanket Octopuses carry around tentacles from one of the most potent stinging jellyfish.
Octopus nunchucks (a.k.a. stolen stinging tentacles)
Scientists had noticed what looked like jellyfish tentacles on the arms of young Blanket Octopuses as early as 1857, but the source of the tentacles and the octopus’s deliberate use of them as weapons were only confirmed in 1963. The tentacles belonged to the Portuguese Man O’ War, a colonial jellyfish relative called a siphonophore.
A scientist at sea caught a juvenile blanket octopus in a net, picked it up with his bare hand, and was so severely stung that he “involuntarily threw the octopus back into the water.”
Most humans would have proceeded to avoid the animals, but he promptly collected a dozen more and “purposely placed each one on the tender areas of my hands.” The pain recurred, and through careful study, he discerned its cause–fragments of Man O’ War tentacles, carried in the octopus’s suckers!
How does the Blanket Octopus grab these stinging tentacles?
Perhaps through “pickpocket dexterity,” as the scientist suggested; or perhaps after eating the rest of the jellyfish. The young octopus may use them for prey capture as well as self-defense.
Have you seen an octopus hitchhiker before?
Whether you are a Portuguese Man O’ War or an Australian spotted jellyfish, it would seem that picking up an octopus hitchhiker is a risky prospect. The best outcome you can hope for is not to be eaten; the worst is that it’ll tear off your arms and slurp the food right out of your stomach.
Luckily for the human photographers who record these visually stunning octopus-jelly interactions, it’s unlikely that any gelatinous creatures are reading this article or acting on the advice therein.
Special thanks to Danna Staaf!
Thank you to Danna for sharing her knowledge about argonauts, the magnificent octopus hitchhikers grabbing rides on jellyfish & other fun things!
Danna Staaf is a cephalopod scientist and author, with a new argonaut-focused book coming in October. The Lady and the Octopus: How Jeanne Villepreux-Power Invented Aquariums and Revolutionized Marine Biology is now available for preorder, and Staaf will be sharing more wild and wacky argonaut stories with OctoNation in the months to come!
If you want to educate yourself some more about all sorts of different cephalopods, take a look at our encyclopedia. Or, what we call it, our Octopedia!
Connect with other octopus lovers via the OctoNation Facebook group, OctopusFanClub.com! Make sure to follow us on Facebook and Instagram to keep up to date with the conservation, education, and ongoing research of cephalopods.
More Posts To Read:
- A Dreaming Octopus? Let’s Look At Cephalopod Sleep Cycles!
- Does An Octopus Have Arms Or Tentacles?
- The Fantastic Phore: Cephalopods Color-Changing Abilities!
- Here’s Everything You Need To Know About Octopus Arms
- 7 Jaw-Dropping Caribbean Reef Octopus Facts
- Argonaut chains: https://academic.oup.com/icesjms/article/67/7/1494/661868?login=true
- First report of argonauts in salps: https://oceanrep.geomar.de/id/eprint/37578/7/2071.pdf
- Argonaut biting into jellyfish stomach: https://www.jstor.org/stable/pdf/24831832.pdf?casa_token=5ddwIan4LLwAAAAA:GtJlFxwqTnOW321jAdEABwfozWZq3UryzooNQSXaenYaywmOOWMJDyW1z-81yiO1r3Rn4QgZ u9Vs1caBPm2bzgalisZYR8gYrD2zsEQ4650JXOXlzdS
- Blanket octopus using man-o-war tentacles as weapons: https://www.jstor.org/stable/1710225?seq=1