How related are they?
Same genus, Mithraculus (Clinging crabs): very close cousins
They split at the species level: the Spider Crab belongs to Mithraculus forceps (Red-ridged Clinging Crab), the Emerald Crab to Mithraculus sculptus (Emerald Crab).
Find the Spider 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 | Spider 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 | Mithracidae Mithracid spider crabs | |
| Genus | Mithraculus Clinging crabs | |
| Species split | Mithraculus forceps Red-ridged Clinging Crab | Mithraculus sculptus Emerald Crab |
Care, side by side
| Fact | Spider Crab | Emerald Crab |
|---|---|---|
| Type | Invertebrate · Crab | Invertebrate · Crab |
| Care level | Easy | Easy |
| Reef safe | With caution | Yes |
| Temperament | Peaceful | Semi-aggressive |
| Diet | Omnivore | Omnivore |
| Favorite foods | Hair and film algae, Bubble algae, Macroalgae | Bubble algae (Valonia), Mysis shrimp, Dried seaweed (nori) |
| Max size | 1 in (2.5 cm) | 2 in (5.1 cm) |
| Minimum tank | 26 gal | 20 gal |
| Temperature | 72–82 °F | 72–80 °F |
| Salinity (SG) | — | 1.023–1.025 |
| pH | 8–8.3 | 8.1–8.4 |
| Lifespan | 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 |