For the first time ever, a hermit crab has been documented to have found its “forever” home. Off the coast of Japan, a new species of the crab has partnered with a living coral. The coral grows as the crab ages, which means it has no need to continue searching for a bigger shell to live in. Unlike its counterparts, this new species has a perfectly symmetrical body to fit the coral that grows with it.
The discovery of the Diogenes heteropsammicola is described in the journal PLOS ONE. This is the first species of hermit crab to live within “walking coral,” a free-living variety of coral that grows as tiny lumps on the sea floor.
This relationship has been witnessed before, but usually between the peanut worm (or more formally, a sipunculan) and the living coral. Because the coral protects the worm and the worm carries the coral around the sea floor, it is considered to be a mutually beneficial partnership. Both species are in sync with each other, as their relationship has evolved for thousands of years.
As IFLScience points out, that makes this latest discovery even more amazing — and unusual. It is relatively unheard of for one species to diversify to include other organisms, such as the coral has done with the hermit crab. This is because the initial partnership often requires an extraordinary amount of specialization.
Nonetheless, the coral has accepted the crab, likely because the crustacean carries the coral around the sea floor and prevents it from being covered in sediment. In turn, the coral protects the small creature. This is definitely an improvement upon hermit crabs adopting discarded bottles and pollution as their new homes.
Images via Momoko Igawa, Igawa et al. 2017