How related are they?
Same genus, Mithraculus (Clinging crabs): very close cousins
They split at the species level: the Emerald Crab belongs to Mithraculus sculptus (Emerald Crab), the Spider Crab to Mithraculus forceps (Red-ridged Clinging Crab).
Find the Emerald Crab on the tree · Find the Spider 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 | Emerald Crab | Spider 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 | Mithracidae Mithracid spider crabs | |
| Genus | Mithraculus Clinging crabs | |
| Species split | Mithraculus sculptus Emerald Crab | Mithraculus forceps Red-ridged Clinging Crab |
Care, side by side
| Fact | Emerald Crab | Spider Crab |
|---|---|---|
| Type | Invertebrate · Crab | Invertebrate · Crab |
| Care level | Easy | Easy |
| Reef safe | Yes | With caution |
| Temperament | Semi-aggressive | Peaceful |
| Diet | Omnivore | Omnivore |
| Favorite foods | Bubble algae (Valonia), Mysis shrimp, Dried seaweed (nori) | Hair and film algae, Bubble algae, Macroalgae |
| Max size | 2 in (5.1 cm) | 1 in (2.5 cm) |
| Minimum tank | 20 gal | 26 gal |
| Temperature | 72–80 °F | 72–82 °F |
| Salinity (SG) | 1.023–1.025 | — |
| pH | 8.1–8.4 | 8–8.3 |
| Lifespan | About 2-4 years in captivity per one care guide (Aquariadise); no published data. | No published data. |
| Breeding | Hard | Hard |
| Conservation (IUCN) | Not Evaluated | Not Evaluated |