Polka Dot Hermit Crab
The Polka Dot Hermit crab will eat hair algae and scavenge in your aquarium. It has a relatively large white claw that it uses to close the shell it is in when it is retracted, giving the appearance there is a snail inside. While Polka Dot Hermit Crabs will not eat your corals, they may attack snails for their shells, and this is something to be mindful of in your tank. You can reduce this risk by having plenty of empty shells for them to move into. They are good cleaners, but they aren't particularly cost effective.