Sabellarian tubes as the housing of the hermit crab Discorsopagurus schmitti.

Discorsopagurus schmitti (Stevens, 1925) has been reported as the only crustacean decapod that both ecologically depends on and zoogeographically is restricted to worm bioherms. This species lives exclusively inside empty Sabellaria cementarium tubes, and actively chooses them when also presented with gastropod shells in the laboratory. The fascinating question arises as to why this species (presumably descended from shell-carrying ancestors) turned to this unusual housing, which has also caused the appearance of new modes of behavior and the evolution of a sedentary life-style.