Crabs are one of the largest groups of crustaceans, and the most diverse in both shape and size. The group’s scientific name, Brachyura, means 'short tail', and refers to the major evolutionary breakthrough that has made crabs so successful. Instead of using the tail for swimming, crabs have it greatly reduced and tucked completely under their body (carcinisation), and no longer have a tail-fan. This gives them a compact body shape and increased mobility, allowing them to spend their adult lives in a variety of habitats on the sea floor. Though some shore crabs can run sideways at great speed, most crabs can move in any direction they choose, belying the popular myth.

Considered to have first appeared in the Jurassic period (144-213 million years ago), the world fauna is now known to consist of more than 7000 species, of which nearly 1200 are known from Australia. The majority of crabs live in shallow marine environments, but others occupy a huge variety of habitats, ranging from deep-sea hydrothermal vents to tropical rainforests, freshwater streams, and even inland deserts. While important commercially, the crab fishery is dominated by a few members of a single family, the Portunidae, which includes Mud Crabs (Scylla species), and the Blue Swimmer Crab (Portunus armatus). More than half a million tonnes of these crab are caught and eaten each year in the Indo-West Pacific region. Examples of Queensland crabs include:

• Red and White-spotted Reef Crab (Lophozozymus erinnyes)
• Orange-clawed Fiddler Crab (Tubuca coarctata)
• Soldier Crab (Mictyris longicarpus)
• Spanner Crab (Ranina ranina)
• Cleft-fronted Bait Crab (Guinusia dentipes)
• Common Box Crab (Calappa hepatica)
• Speckled Sand Crab (Ashtoret lunaris)
• Shawl Crab (Atergatis floridus)
• Blue Coral Crab (Trapezia cymodoce)
• Honeycomb Coral Crab (Trapezia septata)
• Coral Swimmer Crab (Charybdis [Charybdis] feriata)
• Hairy Swimmer Crab (Charybdis natator)
• Stalk-eyed Swimmer Crab (Podophthalmus vigil)
• Sand Crab or Blue Swimmer Crab (Portunus armatus)
• Three-spotted Swimmer Crab (Portunus sanguinolentus)
• Two-toned Fiddler Crab (Gelasimus vomeris)
• Mud Crab (Scylla serrata)
• Furry-clawed Crab (Australoplax tridentata)
• Giant Sentinel Crab (Venitus latreillei)
• Horn-eyed Ghost Crab (Ocypode ceratophthalmus)
• Smooth-handed Ghost Crab (Ocypode cordimana)
• Semaphore Crab (Heloecius cordiformis)
• Sand Bubbler (Scopimera inflata)
• Purple Swift-footed Shore Crab (Leptograpsus variegatus)
• Shiny Bait Crab (Davusia glabra)
• River Swimming Crab (Varuna litterata)