It’s the cohabiting arrangement previously undocumented by science; a modern day The Odd Couple but stopping short, perhaps, of Will & Grace. This is the discovery of a new species of tusk shell and its living arrangement – in a region below 3,300 metres known as the abyss – with the anemone that resides on its shell.

A never-before-witnessed arrangement at these kinds of depths, the discovery of the almost-harmonic lifestyle shared between the burrowing marine mollusc and the anemone was made by scientists from both the British Antarctic Survey and the Senckenberg Society for Nature Research as part of their ongoing exploration of deep North Atlantic waters.

Hailed as one of science’s rarest discoveries, what makes this finding so special is that this is the first time a tusk shell burrowing mollusc – this newly described Fissidentalium aurae – has been observed in a ‘mutualistic’ arrangement with an anemone outside of the Pacific Ocean.

But the relationship is not all smooth sailing. In fact, the anemone – it was observed – acts as somewhat of a hindrance on the tusk shell’s ability to burrow to the same depths it would without the co-habitant on its back, leaving it more open to predators. So why not call the whole thing off? Well, the same researchers suggest the anemone does pull its weight in other ways, by warding off potential predators with its tentacles.

Meanwhile, the anemone is having a time of it. A marine species usually found stationary, this anemone is able to ride the mollusc’s back to reach new food sources and nutrients in what is typically a region deficient in food. All it asks is the mollusc doesn’t burrow too deep and risk harming the anemone.

This new species of mollusc was discovered during an expedition between north-eastern Canada and western Greenland, where the team collected several specimens from the seafloor and many more were observed using seafloor imaging. The red and white individuals measured an average of 1.1cm in diameter and 5.5cm long, making the species larger than other closely related tusk shells.

The description of Fissidentalium aurae was published in the journal Springer Nature and led by the British Antarctic Survey’s senior biodiversity biologist, Katrin Linse who said the discovery “serves as a reminder that we know so little about life in the deep, particularly the way it adapts and how species pull together to benefit from each other’s presence.”

To investigate life on the abyssal ocean floor, Linse and her colleagues aboard the RV Sonne used a small net, known as an Agassiz trawl, which can be deployed thousands of metres deep to collect samples from the floor of the Labrador Sea.

The new species of mollusc is a member of the genus Fissidentalium which currently has over 60 known species. It was named aurae after the Latin word for breeze, referring to the windy conditions during the expedition.

The study’s co-author, Jenny Neuhaus, a PhD student at Seckenberg, sampled DNA form the anemone and checked its genetic barcode against all known barcodes in genetic databases. The test resulted in no close match. 

The position of the anemone in the tree of life and its scientific name is a riddle still be be solved.

“The discovery of this beautiful species shows that the deep sea never ceases to surprise us,” said Neuhaus. “Not only is it fascinating to scientists to find a new species, but also sparks curiosity in the general public.”

Earlier this month, the team’s research earned itself a science award from the maritime city of Wilhelmshaven in Germany.

“We are grateful for this recognition, which emphasises the importance of collaborative efforts in deep-sea research,” added Neuhaus.

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