The crab itself has reddish and black lines extending the length of its legs. They are very active and should be fed daily. These crabs are great scavengers for large fish-only tanks. Multiple Black Scarlet Hermit Crabs can be kept per tank. Crabs belong to the Class Crustacea and Order Decapoda. Hermits belong to the Section Anomura, which consists of long antennae and three pair of walking legs.