Emerald Crab (Mithraculus sculptus)

Emerald crabs have carved out a reef-tank reputation as the go-to answer for a bubble algae bloom — broad, flattened claws built for shredding Valonia clusters that most other cleanup crew members leave alone. That specialization comes with a catch: like every crustacean it goes through periodic molts to grow, and a freshly molted emerald crab is soft-shelled and vulnerable for a day or two, so don't be alarmed if it vanishes into the rockwork right after you spot a shed exoskeleton drifting in the current.

Care level: Easy · Temperament: Semi-aggressive, generally reef safe · Max size: ~2" · Min tank: 10 gal · Diet: Omnivore, algae/leftover food