SYNOPSIS. AS an ecotone, the littoral environment is often complex and is generally rich in numbers and species of organisms. The disadvantages of the biotope in terms of exposure to physical factors of both the marine and terrestrial environments are patent, but the advantages are not so evident. The continual replenishment of food brought from the sea, particularly for detritus-feeding animals such as hermit crabs, coupled with the possibility and ability to establish microhabitatswith microclimatic conditions may constitute the principal advantage. Escape from specialized predators may also be important. Hermit crabs have successfully exploited most intertidal environments. As members of the “benthic detritus-feeding guild” food is abundant, and by utilizing their shells in conjunction with movements within the littoral zone they have met successfully most of the rigors of the environment. The shell also provides some protection from predation, particularly from non-specialized predators.Indeed, the behavioral patterns associated with living in shells which permit the shell to serve as a microhabitat constitute the major adaptation enabling the hermit crabs to exploit the intertidal environment so successfully.