Eriocheir

Eriocheir is a genus of freshwater crabs in the family Varunidae, commonly known as mitten crabs because the inner surface of the first pair of legs bears dense patches of setae that resemble mittens. They are medium-sized decapods with broad, rounded carapaces and robust claws; males typically have larger claws and more pronounced chelae.

Native to East Asia, the genus includes several species, the most widely known being the Chinese mitten crab, Eriocheir sinensis. Eriocheir crabs inhabit estuaries, rivers, and streams and can tolerate a range of salinities from freshwater to brackish water.

Ecology and life cycle: They are omnivorous, feeding on mollusks, crustaceans, detritus, and plant matter. They are catadromous: adults migrate downstream to brackish or marine waters to spawn; eggs hatch into free-swimming zoea larvae that develop in the sea, after which juveniles migrate upstream into freshwater habitats.

Invasive status and impact: Eriocheir sinensis has established populations outside its native range, particularly in Europe and North America, where introductions are linked to ballast-water discharge and aquaculture. In non-native areas, mitten crabs can compete with native crabs, predate on local fauna, damage vegetation and riverbanks, and clog waterways. Management efforts include trapping and public reporting.

Taxonomy and notes: The genus is placed in Varunidae, with historical placement in Grapsidae in older classifications. Distinguishing features include the mitten-like setae on the male chelae and a broad, oval carapace. The taxonomic status of some East Asian species has changed with revisions to the group.