New Anemone Species Acts As A Fabulous Hat For Hermit Crabs

Their obligate symbiotic relationship means one can't live without the other.


Rachael Funnell

Social Editor and Staff Writer

clockAug 5 2022, 10:01 UTC
hermit crab anemone hat
As hats go, this one is pretty special. Images courtesy of Akihiro Yoshikawa from

Have you ever loved a fashion accessory so much that you would die without it? The hermit crab Pagurodofleinia doederleini certainly understands the sentiment, as it was recently discovered that its survival depends on a new-to-science anemone that it wears as a hat that serves in both fashion and function.


The new species of anemone, found on the seabed off Japan, has been named Stylobates calcifer, inspired by Studio Ghibli's Howl’s Moving Castle character Calcifer, everyone’s favorite fire demon. “The shell-making ability of the new species in the species-specific relationship appears as if Calcifer was in a magical contract with the Wizard Howl, constructing his Moving Castle,” explained the authors of the paper published in The Biological Bulletin.

The anemone was already known in Japan and had a Japanese name, the Himekinkara sea anemone, but hadn’t yet been recognized academically. Now it's officially on science's hermit crab roster, and it's got a cool second name to boot.

Crustaceans with hats have been a running theme in recent novelty animal news, as scientists recently named a new species of absurdly fluffy crab that trims sea sponges into berets. The living hats are thought to protect the fuzzball crustaceans from predators, and the same protective effect is believed to be true of the rather more radical hats of Japan’s fashion-forward hermit crabs.

The anemone can be open and wavy, but it also has a beanie mode.


The relationship between the hermit crabs and their anemone hats is thought to be a serious one, falling into the “obligate symbiosis” category according to the researchers who believe the two species need the other to survive. The urgency was certainly reflected in the recorded behavior of one hermit crab who was filmed painstakingly pinching and massaging its beloved anemone until it was detached so they could move it onto their new shell.

Moving house like this comes at no small cost to the hermit crabs either, as the anemones weren’t always cooperative. In one observation, the crab tried to encourage the anemone to sucker onto a new shell for 12 hours without success, and eventually had to go back to the old one.

It later tried again and was successful, but the overall process represented 43 hours of work on the part of the hermit crab. A lot of work, then, but perhaps worth it considering that as well as looking fresh to death, its efforts mean it’s protected from parasites and predators.

The hermit crabs put in a lot of work convincing the anemones to move home.

The living anemone hat benefits two-fold from its lofty position, firstly from having a decent spot from which to catch delicious falling ocean debris. Secondly, riding on the roof of what’s essentially the hermit crab’s RV means it gets year-round access to fresh feeding grounds.

Curiously, some hermit crabs of the species were seen without anemones, which the researchers suggest may have been the result of crustacean crime. The dependency of the hermit crabs on their Calcifer bonnets as a means of survival may be enough to motivate stealing, however further research is needed to confirm this.


While the research is limited in its sample sizes, it demonstrates that living hats is an apparent trend among crustaceans.

“Because of our limited observations due to difficulties in collecting specimens, we conducted all behavioral observations on a single specimen,” explained the authors. “Nevertheless, our behavioral observations are suggestive of the remarkable symbiotic relationships in the actiniarian CF mutualisms in the deep sea.”

[H/T: Mongabay]

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