A white octopus sat on the sea floor, gently rocking its short arms and staring with beady eyes at the camera of a deep-diving robot.
It was 2016, in the waters off Hawaii, at a depth of 4,290 meters (2.6 miles). No one has seen an octopus like it before, and certainly not that deep. Based on his ghostly appearance, he was called Casper.
Until then, the only cephalopods that had been photographed at such depths were Dumbo octopusnamed after another cartoon character, were seen swimming as deep as 6,957 metres, with elegant ear-like plates on either side of their heads.
Watching Casper was an amazing moment for Janet Voight, associate curator of invertebrate zoology at the Field Museum of Natural History in Chicago. “This is completely new and different,” she says, recalling the discovery.
That first glimpse of Casper revealed many perplexing mysteries. Why is he so pale? Most other octopuses have colorful 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, such as purple, warty graniledon. Some use a cloak of dark skin pigments, apparently to disguise the glowing, bioluminescent prey they hold in their arms and thus avoid alerting other predators. Voight speculates that Casper’s pallor may be due to a lack of pigments in his food.
Another mystery 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 will be,” Voight says.
This trend towards shorter arms in deep octopuses has no clear explanation. Voight believes that rather than stretching out to get food, they have developed an alternative tactic of rolling their bodies so that their mouths, on the underside of their bodies, are directly above their food.
Scientists have learned more about Casper by searching five years of archived footage collected in deep-sea surveys across the Pacific Ocean. They have discovered dozens like Casper perched on the sea floor, of two distinct species.
“It can be fairly common,” Voight says. “It’s just an indication of how little we know what’s below.”
For Voight, it was especially exciting to have Caspers with arms wrapped around clutches of eggs glued to long sponges. Previously, she had assumed that octopuses living on the sea floor needed solid rocks to lay their eggs on. Moreover, there can be fewer exposed rocks, which limits its depth.
“Casper showed that there are ways to get around this by finding a sponge leg,” she says. “Is this a breakthrough in octopus evolution?”
The sponges themselves are associated with rock nodules scattered across swaths of the abyssal plains and take millions of years to form.
If it’s anything other deep-sea octopuses go through, it’s likely that female caspers spend a significant amount of time guarding their eggs. another type of octopusGraneledone boreopacifica) off the coast of California, on a steep cliff in Monterey Canyon, she eats her only clutch in the exact same spot. For more than four years.
At the moment, the pale and mysterious Casper octopuses have not yet been officially named, because everything we know about them comes from the photos; No one was able to collect a sample for the study in detail.
“With the octopus, you really need it on your hand,” Voight says.
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