thumbing through my invertebrates reference guide, i came across a crab that kind of looks like your new fella,i don't know how to post it's picture yet, but you could go under yahoo, or google and probly find it. it's called a (calcinus) common name red leg hermit crab. species have unequal sized claws,(the left is usually larger) and long eyestalks.they occur in tidepools and on reefs. it's similar to the paguristes. the book says it is reef safe useful in aquariums,
herbivorous. good for algae control, feeds on filamentous algae and cyanobacteria. also carnivorous.
may attack and kill snails eating them and taking there shells.you can feed them dried seaweed (nori).
life span years.
i don't know if this is what yours is but it sure looks like it from your picture. good luck.
tonya-sr