Last week, a remotely operated vehicle (ROV) surveying the depths off the northern Great Barrier Reef encountered a mysterious cylinder hanging vertically in the dark water around 2,790 feet. “It looks like a pale eggplant,” remarked one of the ocean enthusiasts who had tuned in to watch a live video feed of the dive.
While that may not sound like a flattering first impression, that pale eggplant turned out to be an elusive species of squid that had never before been caught on camera in the wild, reports Nicoletta Lanese for Live Science.
Exciting news! This appears to be the FIRST observation of Spirula, aka ram's horn squid, alive + in its natural environment. Very rarely seen or captured, they have many extinct relatives, but are only living member of genus Spirula, family Spirulidae, and order Spirulida. 1/3 pic.twitter.com/re4rZyRuER— Schmidt Ocean (@SchmidtOcean) October 27, 2020
"I've been looking for these for a long time," Michael Vecchione, a squid researcher at the Smithsonian National Museum of Natural History, tells Carly Cassella of ScienceAlert. "I have no question at all it's a Spirula."
Neige Pascal, who studies squid at the University of Burgundy in France, tells ScienceAlert the video is "very exciting.”
Both researchers echoed the fact that they’d never seen footage of the small, roughly two-inch squid in the wild. Inside the squid’s oblong mantle lies a multi-chambered spiral shell that looks something like a miniature nautilus shell. That shell is part of what makes the ram’s horn squid special.
They’re the only living species of cephalopod with a coiled internal shell, which regulates the animal’s buoyancy with bubbles of gas, reports Sabrina Imbler for the New York Times. Though their owners have been anything but a common sight for undersea explorers, these whorled shells are commonly found by beachcombers around the world, according to ScienceAlert.
Like many marine creatures that inhabit a world almost completely devoid of sunlight, the ram’s horn can make its own light—the squid sports a bright green photophore on its rear, per the Times.
The sighting of this tiny squid in its gloomy habitat also managed to clear up an aspect of its behavior that had previously puzzled researchers. Whenever the ram’s horn showed up in trawl nets or was brought to the surface for study, their mantles would bob up, orienting the squid with its tentacles facing down. This orientation made some sense in terms of buoyancy, with the gas-filled shell floating above the rest of the body. But that pose would point the ram’s horn’s photophore up towards the surface, and other creatures tend to shine their bioluminescence toward the seafloor to obscure their silhouette and make it harder for predators to spot.
The notion that the ram’s horn pointed its green light skyward “is neither common nor does it make sense,” Vecchione tells the Times.
However, this latest sighting in the squid’s natural habitat turns that confusing observation upside down. In the video, the squid is clearly facing tentacles up and mantle down, which Vecchione tells the Times “makes sense.”
Though the undersea sighting may resolve the question of how the photophore works, other researchers wondered how the ram’s horn was able to hover vertically in the water column with the buoyant part of its body underneath it. “You'd think the head, which is heavier, would be hanging down,” Vecchione tells ScienceAlert. The answer here may come from more detailed analysis of the squid’s flapping fins, which can be seen in the video.
The ROV, called SuBastian, that spied the ram’s horn was conducting research for the Schmidt Ocean Institute. The day before collecting the inaugural video of the squid, SuBastian discovered a coral reef taller than the Eiffel Tower, as it mapped the Cape York Peninsula at the far northern end of the Great Barrier Reef in Australia.