Scarlet Hermit crab
Scarlet Hermit Crabs are useful to keep corals and live rock clean of nuisance algae. They also help process detritus, stir the sand, and give you hours of enjoyment watching them navigate through your reef tank carrying their home on their back. I have a few of these and they do no harm. Hermit crabs are known to be opportunistic, and can kill a snail to steal the shell for a newer larger home. Reef-safe.