Crab and coral make a deal

archive – Diving NewsCrab and coral make a deal

A new species of hermit crab has been discovered in southern Japan – but instead of making its home in discarded shells, it has come to an arrangement with “walking” corals.

The coral hermit crabs, dubbed Diogenes heteropsammicola, have been studied in shallow waters in the Amami Islands by scientists Momoko Igawa and Makoto Kato from Kyoto University. 

Symbiotic relationships between solitary corals and sipunculan marine worms are familiar to marine biologists. The so-called walking coral, which lives on soft seabeds, grows over and envelops gastropod shells to form an internal coiled cavity in which the worm can live and provide the coral with the ability to move around. But such a relationship involving a crab had never been observed before.

The crab inhabits the cavity within Heterocyathus and Heteropsammia corals, and the exchange of services is straightforward.

The crab provides legs for the coral which, carried as it is above the seabed, can avoid becoming buried in shifting sand or overturned by currents.

For the crab, the coral provides a home which, unlike a shell, it won't grow out of, because the two “symbionts” go on growing together.

The coral also has a sting that helps to protect the crab from predators.

The research is published in Plos One here.

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