Emerald Crab

Looks how to spot one

Hard, flat carapace with hairy legs

A small crab with a flat, glossy, deep green shell (about 1.2 cm across the carapace) and paler, hairy walking legs. The claws have white tips. Its strong legs let it grip rock very firmly.123

Personality what they are like

Semi-aggressive by nature but usually easygoing when well fed.3

Daily activity how busy a day looks

Mostly nocturnal, hiding in crevices by day and scavenging at night.13

Grooming and care the hands-on bits

Easy to keep. Add seaweed, meaty foods and pellets so it stays well fed, and keep water stable and copper-free.3

Home where they are happiest

An established marine reef aquarium with plenty of rockwork and hiding places. LiveAquaria gives 72-78 °F (about 22-26 °C), pH 8.1-8.4, dKH 8-12 and specific gravity 1.020-1.025. Wild crabs live on reefs and in seagrass from the shallows to about 55 m. No minimum tank size was given by the sources.32

Food basics what goes in the bowl

Omnivorous scavenger that eats algae (including bubble algae) and leftover meaty foods.13

Company who they like around

Can live with most reef tankmates when well fed. In the wild it sometimes associates with sea anemones.32

The story where it all began

The emerald crab was described by Lamarck in 1818 from the western Atlantic. Reef keepers adopted it as a natural helper against bubble algae, a use supported by research.21

Recognised by the official bits

Taxonomy (via SeaLifeBase)

Described by Lamarck in 1818 (originally as Maia sculptus).2