A white octopus sat on the sea floor, gently moving its short, thick arms and staring with bright eyes into the camera of a deep-diving robot.
It was in 2016, in the waters off Hawaii, at a depth of 4,290 meters (2.6 miles). No one had ever seen an octopus like this, and certainly not this deep. Based on his ghostly appearance, he was nicknamed Casper.
Until then, the only cephalopods filmed at these depths were the Dumbo octopuses, named after another cartoon character, which were seen swimming as deep as 6,957 meters, with elegant ear-like fins on either side of the head
Casper’s sighting was a surprising moment for Janet Voight, associate curator of invertebrate zoology at the Field Museum of Natural History in Chicago. “This is totally new and different,” he says, recalling the discovery.
That first glimpse of Casper led to many tantalizing mysteries. Why is he so pale? Most other octopuses have colored chromatophores in their skin that change their appearance in an instant and act as camouflage to confuse predators.
Even in the deep sea, octopuses can be colorful, like purple, warty graneledone Some use a layer of dark skin pigments, apparently to hide bright, bioluminescent prey they grab in their arms and thus avoid alerting other predators. Voight guesses that Casper’s paleness may be down to a lack of pigments in his food.
Another puzzle is the short arms, although Casper isn’t the only one with limited reach. “The more shallow and tropical you are, the longer and thinner your arms are,” says Voight.
This trend toward shorter arms in deep octopuses has no definitive explanation. Voight thinks that instead of stretching to grab food, they developed an alternative tactic of turning their bodies so that their mouths, on the lower part of their bodies, are directly over the food.
Scientists have learned more about Casper by combing through five years of archived images collected in deep Pacific surveys. They saw dozens more like Casper lying on the seabed, of two different species.
“They could be quite common,” says Voight. “It’s just an indicator of how little we know about what’s down there.”
For Voight, especially exciting were the Caspers with their arms wrapped in eggs stuck to tall sponges. He had previously theorized that octopuses that live on the sea floor need hard rocks to lay their eggs on. Further down, there could be less exposed rock, limiting how deep they can go.
“Casper showed that there are ways around this by finding a sponge stem,” he says. “Is this a breakthrough in the evolution of pop?”
The sponges themselves are attached to rock nodules that are scattered across swaths of abyssal plains and take millions of years to form.
If other deep-sea octopuses are present, female Caspers probably spend a lot of time guarding their eggs. An octopus of another species (Graneledone boreopacifica) was spotted off the coast of California, on a craggy bluff in the Monterey Canyon, brooding her only clutch in exactly the same spot for more than four years.
At the moment, Casper’s pale and mysterious octopuses have yet to be officially named, because everything we know about them comes from imagery; no one has been able to collect a specimen to study it in detail.
“With an octopus, you really need it in your hand,” says Voight.
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