Hermit crabs in general are useful members of the aquarium cleanup crew.
The Blue Leg Hermit Crabs (Clibanarius tricolor) are especially prized because they eat film algae, hair algae and even some kinds of cyanobacteria.
While all hermit crabs pose some level of risk to snails, this is one of the least aggressive types in our experience. The very small specimens we carry are even less of a threat to snails because of their snail size.
These crabs generally occupy small dark Cerith Snail shells like the ones pictured here, but this varies from one specimen to another. These are under 1/2 inch in length.