An underwater photographer has stumbled upon a new species of hermit crab with legs and pincers striped like candy canes.

Ellen Muller captured photos and video of the tiny creature at dive sites in the National Marine Park off the southern Caribbean island of Bonaire. Just a few millimetres wide, the animal is the subject of a new report in the journal ZooKeys

The report is authored by the Smithsonian's Rafael Lemaitre, a hermit crab expert who documented the new species.

The red-and-white colour pattern on the legs and pincers of the crab reminded both Lemaitre and Muller of a traditional candy cane, prompting them to give it the common name "candy-striped hermit crab."

Its scientific name is Pylopaguropsis mollymullerae, after diver Muller's young granddaughter, Molly Muller.

An accidental discovery

On one of her dives, Muller photographed a flaming reef lobster, a popular subject for underwater photographers because of the creature's bright colour, said Lematire.

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Diver and underwater photographer Ellen Muller was taking photos of this flaming reef lobster when she also captured the previously undiscovered hermit crab. (Ellen Muller)

Muller sent her photographs to crustacean expert Arthur Anker so he could examine the lobster.

"Just by accident there was a little hermit crab in the corner of the photograph," Lemaitre said.

Hermit crabs are soft-bodied crustaceans that typically take up residence in abandoned snail shells.

Anker recommended that Muller send her images to Lemaitre, who specializes in the creatures.

"I immediately realized it was something unusual," said Lemaitre, who asked her to take more photographs during subsequent dives.

candy-stripe-crab-lemaitre

The Smithsonian's Rafael Lemaitre — seen with a collection of hermit crab specimens — estimates he's discovered around 100 new species during his 30-year career.

Hanging with the eels

"She discovered some individuals of this hermit crab were hanging around these big moray eels," he said. This set of photographs left him more confident the crabs were not yet documented, Lemaitre said.

On one of her dives, Muller captured video of one of the crabs crawling on a moray eel.

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Images and video of the crab crawling on and around a moray eel could mean the two species have a symbiotic relationship where the crab cleans and feeds off the eel, unique among hermit crabs discovered so far. (Ellen Muller)

This was significant because it suggests the two very different animal species might have some sort of "ecological association," Lemaitre said.

It's common for other types of crustaceans, like shrimp, to act as cleaners for larger animals, feeding off mucus and other materials that collect on their bodies. But hermit crabs have never been reported to act as cleaners, he said.

Shrimp swim around the sea creatures they clean. Crabs don't swim — they crawl.

"However, moray eels are like snakes," said Lemaitre. "They hang around the bottom all the time, so it would be easy for these hermit crabs to crawl on their bodies."

At this early stage in their discovery, it's still speculation whether the candy-striped hermit crab is indeed a cleaner. "If that's the case then it's a very interesting discovery," he said.

A crab named Molly

After obtaining permits from the government in Bonaire, an island municipality of the Netherlands, Muller was able to collect some specimens for Lemaitre to study back at the Smithsonian. There Lemaitre described and documented the animal, establishing that it was indeed undiscovered.

Naming the creature was then up to him.

"I immediately thought to name it after Ellen, because she's the one who observed and noticed the animal for the first time and was kind enough to collect them for me," he said.

This was the second time Muller was involved in helping to discover a new species, she told CBC News in an interview from her Carribean home. Back in 2007, she found a new species of nudibranch, a kind of marine slug.

Since that species was given part of Muller's name, she told Lemaitre she'd prefer the hermit crab to be named after her granddaughter, Molly. "I hope that will inspire her to also take care of the ocean and appreciate life underwater."

'She knows there's a hermit crab that's named after her … but it will take a while until she understands it fully.' - Ellen Muller, underwater photographer

The eight-year-old loves snorkeling and seeing all the fish, said Muller, but hasn't yet grasped the significance of being immortalized in a scientific name.

"She knows there's a hermit crab that's named after her, and she smiles when she hears about it, but it will take a while until she understands it fully," Muller said. 

What's the significance of finding and naming a crustacean just a few millimetres in size? That's easy, Lemaitre said.

"If we don't know what lives out there, how can we protect it? How can we manage our resources and our biodiversity? We need to understand what the pieces are in order to protect the whole."