At a depth of 2560 meters, where sunlight does not penetrate, a crab slowly walks across the abyssal plain.
Its long, thin legs carefully touch the seabed. Its body is almost lost among the sediment, but something amazing rises above its back—a large sea anemone, resembling a living flower.
The crab did not happen to be under it by chance. It holds it with a special hind pair of limbs and carries it along, like an underwater traveler who has taken an entire garden on a journey.
Researchers call the representatives of this family carrier crabs , or porter crabs — carrier crabs. And the crew of E/V Nautilus with a smile compared the sea anemone to the backpack of Dora the Explorer.
But behind this amusing image lies a serious evolutionary mystery.
Why does a crab carry another living creature on itself? Does it use the sea anemone for shelter, camouflage, or protection? And does the sea anemone itself gain anything from this?
The ocean has not yet given a definitive answer. It has simply shown us a scene in which two completely different life forms move together.
Encounter on the Abyssal Plain
On 23 September 2026 , the Ocean Exploration Trust published a video recording made during the expedition NA181 — Exploration of Wake Island’s Deep Sea.
The expedition took place in the area of Wake Atoll — one of the most isolated stretches of land on the planet, located roughly between the Hawaiian and Mariana Islands. Most of the seabed surrounding it still remains virtually unexplored.
Remotely operated vehicles Hercules and Atalanta surveyed the deep-sea plains, seamounts, coral communities and other habitats hidden at a depth of several kilometres.
On one of the dives, the camera spotted a crab of the family Homolidae, holding a large sea anemone above its body.
It is precisely encounters like these that allow us to see the behaviour of deep-sea animals directly in their natural environment — where many processes cannot be reproduced in a laboratory.
Legs That Learned to Hold
In most crabs, the limbs point downwards and help them move along the bottom. But in representatives of the family Homolidae, the last, fifth pair of walking legs is positioned higher than the others, closer to the rear of the carapace.
These limbs are smaller and differently structured. They point upwards and are capable of holding an object above the crab's body.
One could say that, over the course of evolution, an ordinary leg turned into a living holder.
Carrier crabs lift various objects from the bottom:
- sponges;
- corals;
- sea anemones;
- shells;
- parts of the surrounding substrate.
Some representatives of the family carry the chosen object almost constantly. As it moves, the object remains above its back, like a portable canopy or shield.
Thus the animal's body becomes not a finished construction but an open system, capable of incorporating elements of the surrounding space into its own life strategy.
The crab does not grow a protective covering on itself. It finds it in the world — and begins to move together with it.
Why carry a sea anemone
The authors of the video recording name several possible explanations for this behaviour, but emphasise: the precise function in this case has not been established.
Physical camouflage
A large sea anemone alters the crab's outline. From above it may look not like a mobile crustacean but like part of the seabed or a stationary organism.
For a predator that orients itself by the shape of its prey, such camouflage can make recognition more difficult.
Chemical camouflage
In the deep ocean, vision is not always the primary means of perception. Many animals read chemical signals in the water.
Scientists suggest that the organism positioned above the crab may partially conceal or alter its chemical trace. However, with regard to the particular star of the video, this remains a hypothesis requiring verification.
Living protection
Sea anemones possess stinging cells that help them capture prey and defend themselves. If a potential predator tries to attack from above, an encounter with such a "hat" may prove unpleasant.
In this case the crab carries not merely a shelter but a living system of defence.
However, it is still premature to call what was seen a proven mutually beneficial symbiosis. To speak of mutual benefit, it is necessary to establish whether not only the crab but also the sea anemone gains advantages — for example, access to new food flows or the ability to move between suitable patches of the seabed.
The video shows joint movement. The significance of these relations is yet to be determined by science.
Carrying the world with you
The behaviour of the carrier crab is astonishing also because it unites immobility and movement.
A sea anemone usually attaches itself to a surface and waits for the current to bring food. The crab, by contrast, moves in search of resources and shelters. Together they create a new form: the living flower acquires legs, and the moving animal gains a whole protective landscape above itself.
One organism becomes a space for another.
This is not a fusion in which differences disappear. The crab remains a crab, the sea anemone a sea anemone. But their possibilities side by side turn out to be different from what they are apart.
Life often develops in precisely this way. Not only by creating new organs, but also by incorporating into its own system what already exists nearby. Sometimes the evolutionary solution is not to appropriate another's ability, but to be able to build a connection with it.
Not the discovery of a species, but the discovery of a way of seeing
The scientific value of such footage lies not only in the rarity of the animals seen.
Deep-sea submersibles make it possible to observe a creature not separately from its world, but within a whole system of relations: alongside a particular seabed, current, neighbouring organisms and possible sources of food.
A museum specimen can tell us how a crab's limbs are structured. Genetic analysis helps determine its kinship ties. But only observation in its natural environment shows what the animal does with its unusual body.
And here what appears before us is not merely an anatomical feature — a pair of legs raised upwards. We see this possibility in action: the limbs hold another form of life above the carapace.
Form becomes function.
Function becomes behaviour.
And behaviour creates a new connection.
What the ocean reminded us of today
Sometimes the strength of a living system arises from the ability to recognise the qualities of another form and to move alongside it without destroying its uniqueness.
At a depth of 2560 metres, a crab carries a sea anemone above itself. Each of them remains itself, but together they gain a new experience and open up new possibilities.
The ocean reminded us: every form of life is perfect and precious. And in interacting with one another we reveal new facets of what already lives within us.
