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Diogenes heteropsammicola is a species of hermit crab that lives within "walking corals" of the genera Heterocyathus and Heteropsammia.

References

Diogenes heteropsammicola in a walking coral (left) and swimming freely (right)
These coral have an internal cavity that is typically occupied by a symbiotic sipunculan worm; in the crab's habitat in the Ōshima Straight south of Amami Ōshima, it is often found inside the corals instead.