In 2020, about 600 meters (2,000 feet) deep in an underwater canyon off the coast of Western Australia, scientists encountered a long, gelatinous creature suspended in a giant spiral. “It was like a rope on the horizon. You couldn’t miss it,” says Nerida Wilson of the Western Australian Museum. “It was so huge.”
It was a deep-sea siphonophore, a relative of the Portuguese man o’ war, or blue bottle, which bobbed like party balloons on the surface of the sea, trailing deadly tentacles through the water. This was probably a new species of the genus Apolemiaa group that generally look like tangled feather boas.
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The spiral arrangement is known to be a feeding posture in these types of siphonophores. Numerous stinging tentacles create a wall of death in the water, ensnaring small prey, including crustaceans and fish.
Finding it was one of the chance encounters that are common in deep sea research. The scientists’ goal was to study life on the deep seabed, and they stumbled upon this floating jelly as their submersible was a two-hour transit back to the vessel, the research vessel Falkor, then operated by the Schmidt Ocean Institute.
Screens in different parts of the Falkor were showing live footage from the submersible. Wilson describes how everyone on board was both mesmerized and perplexed when the huge spiral appeared. Everyone swarmed into the control room to get a better view. “It was such a beautiful energy,” Wilson says. “Everyone was like, ‘What is this?'”
Time was already short because the dive had gone beyond the scheduled times, and so the pilot of the submarine, controlling it from the surface, was able to spend only a few moments with the animal. “We walked around it, grabbed a few takes and a little tissue swatch,” says Wilson. “Back then we just had to go our merry way.”
Siphonophores look like jellyfish and belong to the same group of animals, but they build their bodies in a unique way, more like hundreds of tiny jellyfish stuck together. However, a siphonophore is a single organism. “He had two parents,” says Wilson. “He was a product of sex.”
Rather than more conventionally growing into a body with organs that perform different functions, siphonophores are made up of individual parts called zooids. Some zooids are responsible for feeding, others for reproduction, and others move and guide the animal through the water. “They’re just one example of how to do things a little differently,” Wilson says. “I am one and I am many.”
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Based on a rough calculation from the submarine track, the spiral-shaped siphonophore is a candidate for the longest specimen ever encountered. At around 45 meters (150 feet), it may also be the longest animal ever measured, much longer than a blue whale.
Reluctant to claim any world records, Wilson is working with a photogrammetry specialist to get a more accurate estimate of the size of the siphonophore. It’s not an easy task to extract three-dimensional information from the video, because the siphonophore moved in the wake of the submersible’s thrusters. “Normally with photogrammetry, you’re going back and forth over a stationary object,” Wilson says. “This is technically a bit more challenging.”