“If you’re afraid of spiders, I’m so sorry to tell you this but you’re not even safe in the ocean,” said OceanX in a viral Instagram post published in October 2024.

According to the researchers who came across this spindly animal on a deep-sea expedition, the species sucks “out the guts of their prey like a smoothie”.

While related to crabs and spiders, sea spiders are invertebrates that have evolved into more than 1,300 different species. They can be found in practically every ocean of the world – at all depths – and while some species measure only millimetres, some can grow as large as dinner plates, according to OceanX.

While most sea spider species have eight legs, some have ten or 12 and not all species have eyes. What all of them have are their spindly legs, however. As their bodies are so tiny, all of their vital organs are located in their long, multi-jointed legs. Its intestines, for example, extend to the end of its legs. Additionally, they not only use their leg exoskeletons to absorb oxygen, they also use their legs to swim and crawl along the seabed without getting stuck in silty environments.

Yet another fun fact about these mysterious animals is that they have an appendage called the ‘proboscis’ which they essentially stab into their soft prey such as worms, jellies, sponges, soft corals, nudibranchs or anemones to suck out their guts and bodily fluids.

As the species is vastly understudied, the video by OceanX’s OceanXplorer vessel is providing vital insights into this mysterious species.

 

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A different research expedition in Antarctica was yet another reminder of how little we actually know of sea spiders. When University of Hawai’i researchers travelled to the region, they were lucky to witness first-hand the reproduction behaviour of giant sea spiders – something that has eluded researchers for over 140 years.

“In most sea spiders, the male parent takes care of the babies by carrying them around while they develop,” UH Mānoa School of Life Sciences Professor and lead researcher Amy Moran said.

“What’s weird is that despite descriptions and research going back over 140 years, no one had ever seen the giant Antarctic sea spiders brooding their young or knew anything about their development.”

While diving in the polar waters, the researchers spotted a group of mating giant sea spiders which they then hand-collected and put into tanks for observation.

Unlike most other species of sea spiders which tend to carry their babies until they hatch, the Antarctic giant sea spiders produced thousands of eggs which one parent – likely the father – laboriously attached to the rocky bottom where they developed for several months before hatching as small larvae.

The research findings were published in Ecology in February 2024.

“We were so lucky to be able to see this,” said School of Life Sciences PhD student Aaron Toh. “The opportunity to work directly with these amazing animals in Antarctica meant we could learn things no one had ever even guessed.”

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