How Many Species of Crabs Are There?

There are more than 7,600 species of true crabs. That figure comes from a 2024 study in Systematic Biology on crab terrestrialisation, which describes the infraorder Brachyura as comprising "over 7600 species" spread across 109 families.

Add the animals that look like crabs but sit outside Brachyura — hermit crabs, king crabs, porcelain crabs — and the total climbs by another two to three thousand. Which number you want depends on whether you mean "crab" in the strict sense or the everyday one.

True crabs versus everything else

Brachyura, the true crabs, is a well-defined group. Members have a broad flattened carapace, a tail folded flat under the body, and four pairs of walking legs plus one pair of claws. Shore crabs, blue crabs, fiddler crabs, spider crabs and the edible crabs sold in fish markets are all in here.

Anomura is a separate infraorder containing several lineages that arrived at a crab-like shape independently. Estimates for its size run from roughly 2,500 to 3,000 species, and it includes hermit crabs, king crabs, squat lobsters, mole crabs and porcelain crabs. King crabs, despite the size and the market value, are anomurans descended from hermit crabs.

Horseshoe crabs are not crustaceans at all. They belong to the Xiphosura, a chelicerate group whose closest living relatives are spiders and scorpions.

| Group | Approximate species | What is in it | | --------------------------- | ------------------- | --------------------------------------------------- | | Brachyura (true crabs) | 7,600+ | Shore, blue, fiddler, spider, edible crabs | | Anomura (false crabs) | ~2,500–3,000 | Hermit, king, porcelain, squat lobsters, mole crabs | | Xiphosura (horseshoe crabs) | 4 | Not crustaceans; related to spiders |

The number has been climbing steadily

The standard catalogue of the world's crabs is Systema Brachyurorum, published by Ng, Guinot and Davie in 2008 in the Raffles Bulletin of Zoology. It listed 6,793 valid extant species and subspecies in 1,271 genera and subgenera, across 93 families and 38 superfamilies.

Set that against the current figure of 7,600-plus and you get roughly 800 species added in about sixteen years — somewhere near 50 new crab descriptions a year, sustained. The family count has risen from 93 to 109 over the same period as molecular work has reorganised the group.

Nobody thinks the count is close to finished. Deep-sea and coral-reef crabs in particular are undersampled, and small cryptic species are still being separated out of what were assumed to be single widespread ones.

Where crabs live

Most crabs are marine, but the group has left the sea repeatedly. The 2024 Systematic Biology study found up to 17 independent transitions out of fully marine life among true crabs, with at least three lineages reaching a high degree of terrestrial adaptation.

Freshwater crabs are the biggest of those radiations. More than 1,300 described species in eight families live in fresh water, and the true total is thought to be considerably higher — possibly up to 2,155 species once undescribed ones are accounted for. They are also among the most threatened invertebrates on Earth: of the freshwater crab species with enough data to assess, around 32 percent are considered at risk of extinction. Many are restricted to a single stream or hillside.

Marine crabs turn up from intertidal rocks to hydrothermal vents. Our random fish generator includes crabs under its ocean filter, alongside the fish and other marine animals.

Why so many things look like crabs

The crab body plan — wide flat shell, tail tucked underneath — has evolved independently at least five times among decapod crustaceans. King crabs, porcelain crabs, hairy stone crabs and coconut crabs each arrived at it from a non-crab ancestor, and the true crabs did it separately.

The zoologist Lancelot Alexander Borradaile named the pattern in 1916, calling it carcinisation and describing it as nature's repeated attempts to evolve a crab. In mechanical terms the shape is a good solution: a compact, armoured body that can scuttle sideways into a crevice, with the vulnerable abdomen protected rather than trailing behind as it does in a lobster or shrimp.

This is also why "crab" as a common name is unreliable. Hermit crabs, king crabs and porcelain crabs are anomurans; horseshoe crabs are not even crustaceans; and crab lice are insects.

What makes counting hard

Three problems recur. Many crabs are small, cryptic and live in habitats that are expensive to sample, so description rates depend heavily on how much survey funding exists. Larvae and adults of the same species often look nothing alike, and were historically described separately. And genetic work regularly finds that a "single" widespread species is actually several with narrow ranges.

The result is that any crab count is a snapshot of taxonomic effort as much as of biological reality. The 7,600 figure is the best current estimate for described true crabs; the number that actually exist is certainly higher.

The short version

More than 7,600 species of true crabs in 109 families, per current literature, up from 6,793 catalogued in 2008. Roughly another 2,500 to 3,000 crab-like anomurans sit outside that group, and horseshoe crabs are not crabs at all.

To draw from across the animal kingdom rather than one group, try the random animal generator.