Sea spiders have been on the planet for at least 425 million years and deep-sea researchers just observed bioluminescence for the first time
When scientists spend a month studying the Australian deep sea, they discovered that two giant sea spiders living in the ocean’s abyssal zone have light-up legs.
The researchers were surveying waters between 1,006 and 4,977 metres deep off Australia’s east coast in May and June 2017 when they found that two species of Pycnogonida (sea spiders) had glow-in-the-dark legs. The discovery is published in Deep Sea Research Part I: Oceanographic Research Papers.
“The Pycnogonida, or sea spiders, have a fossil record extending back to the Silurian period, approximately 425 million years ago,” write the authors in the study. These creatures are categorised within a group called Chelicerata, “which includes animals such as scorpions, horseshoe crabs and spiders among others,” they add.
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Pycnogonids can be found all over the world from shallow coastal waters to the deep-sea. There are more than 1,400 known species currently living on Earth with more being discovered all the time.
Experts are also finding out more about what these strange beings can do. For example, this is the first time scientists have seen Colossendeis tasmanica and Colossendeis minor glowing in the dark. The two species were discovered in 2007 and 1893 respectively.
According to the study, this doubles the number of known bioluminescent sea spiders from two to four.
Seeing the critters glimmer in the deep sea doesn’t necessarily mean they are creating the light – they could be carrying bioluminescent organisms on their bodies.
The researchers examined nine specimens in total and confirmed they can create their own light. “When stimulated by gently pinching the legs, a weak localised glow lasting from a few seconds to more than [two minutes] was induced but with no sign of spreading along the legs,” they write. When they submerged it in a salt bath of potassium chloride, it “triggered a long-lasting blue light from the legs.”
Adding a tiny bit of peroxide (0.1%) to the solution made the light shine even brighter. “All of the legs lit up similarly and mostly at the same time,” they write, and the bioluminescence lasted for up to 10 minutes.
Bizarrely, its body doesn’t produce light. “The species examined here exhibited light emission exclusively from the legs,” say the authors.
The intensity isn’t even all over the legs. The light is dimmer close to the body and gets more intense as it travels down the leg segments. With its dark body and long, spindly legs emanating an eerie blue glow, it looks like an alien spaceship.
Running lots of tests in the lab, they found out that the light was being created in “gut-associated cells within the legs,” which could suggest the radiance might be to do with something the sea spiders are eating.
Scientists still need to study these giant sea spiders more to find out why the animals are producing this mysterious light. They can’t confirm its purpose yet but speculate that it could be for “anti-predation, predation, or reproduction.”
