How related are they?
Same superfamily, Majoidea (spider crabs): relatives from different families
They split at the family level: the Arrow Crab belongs to Inachoididae, the Emerald Crab to Mithracidae (Mithracid spider crabs).
Find the Arrow Crab on the tree · Find the Emerald Crab on the tree
Family lines, side by side
Highlighted rows are groups both animals belong to. The marked row is where their lines go separate ways.
| Rank | Arrow Crab | Emerald Crab |
|---|---|---|
| Kingdom | Animalia Animals | |
| Phylum | Arthropoda Arthropods | |
| Subphylum | Crustacea Crustaceans | |
| Superclass | Multicrustacea | |
| Class | Malacostraca Malacostracans | |
| Subclass | Eumalacostraca | |
| Superorder | Eucarida | |
| Order | Decapoda Decapods | |
| Suborder | Pleocyemata Egg-carrying decapods | |
| Infraorder | Brachyura true crabs | |
| Section | Eubrachyura | |
| Subsection | Heterotremata | |
| Superfamily | Majoidea spider crabs | |
| Family split | Inachoididae | Mithracidae Mithracid spider crabs |
| Subfamily | Stenorhynchinae | — |
| Genus | Stenorhynchus | Mithraculus Clinging crabs |
| Species | Stenorhynchus seticornis Arrow Crab | Mithraculus sculptus Emerald Crab |
Care, side by side
| Fact | Arrow Crab | Emerald Crab |
|---|---|---|
| Type | Invertebrate · Crab | Invertebrate · Crab |
| Care level | Easy | Easy |
| Reef safe | With caution | Yes |
| Temperament | Semi-aggressive | Semi-aggressive |
| Diet | Carnivore | Omnivore |
| Favorite foods | Mysis shrimp and krill, Chopped shrimp and other meaty foods, Small bristleworms | Bubble algae (Valonia), Mysis shrimp, Dried seaweed (nori) |
| Max size | 5.5 in (14 cm) | 2 in (5.1 cm) |
| Minimum tank | 30 gal | 20 gal |
| Temperature | 72–78 °F | 72–80 °F |
| Salinity (SG) | 1.020–1.025 | 1.023–1.025 |
| pH | 8.1–8.4 | 8.1–8.4 |
| Lifespan | About 5 years in captivity per two care guides (Aquarium Source, Build Your Aquarium); several retailers call it long-lived. No published data. | About 2-4 years in captivity per one care guide (Aquariadise); no published data. |
| Breeding | Hard | Hard |
| Conservation (IUCN) | Not Evaluated | Not Evaluated |