How large can malacostracans grow?

Malacostracans, which are a class of crustaceans that includes lobsters, crabs, and shrimp, exhibit a vast range of sizes. While some species are smaller than one millimeter (0.04 inch), others reach impressive dimensions.1

The largest known malacostracan—and perhaps the largest arthropod overall—is the giant crab (Macrocheira kaempferi) of the Pacific waters near Japan. The outstretched claws of this species can measure more than 4 meters (13 feet) from tip to tip. Another notable giant is the Australian sea crab (Pseudocarcinus gigas), which can weigh up to 30 pounds and features a single claw measuring 17 inches in length.23

This diversity in size is a hallmark of the class Malacostraca, which contains more than 29,000 species and represents the most successful and numerous group within the subphylum Crustacea.41