Glowing 'mystery sea slug' that detaches part of its body stuns scientists

Scientists have spotted a "mystery mollusc" within the ocean’s midnight zone. The "sea slug" is a nudibranch that glows, swims, and has an apple-sized body with a paddle-like tail and a large gelatinous hood. It is Bathydevius caudactylus, the first known nudibranch of its kind. Nudibranchs are also known as sea slugs and are soft-bodied marine gastropod molluscs.

The discovery was made by researchers at the Monterey Bay Aquarium Research Institute who say that the sea slug is completely different from other sea slugs. Their discovery has been published in the journal Deep Sea Research Part I and describes the new species.

The sea slug is the first to be found in the deep ocean, more than 7,220 feet below the surface of the Pacific Ocean. Most sea slugs typically live on the seafloor or in coastal environments like tide pools. Only a handful of them live in open water near the surface.

Bruce Robison and Steven Haddock, senior scientists at the Monterey Bay Aquarium Research Institute first spotted the marine creature in 2000 using a subsea research robot during a deep-water dive expedition. Since then, they say that it has been seen more than 150 times.

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Studying the deep midwaters is tough

Scientists have faced challenges studying the deep midwaters because of their depth. They are now hoping that studying the Bathydevius and its adaptations can help them understand more about the midnight zone. Notably, it is the largest habitat on Earth and 70 per cent of all seawater on the planet exists in this region.

“Our discovery is a new piece of the puzzle that can help better understand the largest habitat on Earth," co-lead study author Robison said.

Bathydevius slug's body glows with bioluminescence, putting all its organs on display. The researchers described the slug they had seen in the sea with a large, gaping hood and a fringed tail. It has translucent skin and roseate internal organs which were clearly visible. When it felt threatened, it lit up with a bioluminescent glow.

The scientists say the glow seems to be a defence mechanism, along with something else seen in a familiar reptile. One of the tendrils on the slug's tail glowed steadily, was rotating, and was eventually detached, just like how a lizard leaves its tail behind.