unio

Unio is a genus of freshwater mussels, aquatic bivalve molluscs in the family Unionidae. The genus includes several species native to the Palearctic region, especially Europe and western Asia.

Like other unionids, Unio species have a two-valved shell with a thick, often mottled outer layer and a nacreous inner layer. They are sessile, attaching to hard substrates by byssal threads and feeding by filtering suspended particles from the water.

Unio mussels have a larval stage called glochidia. Female mussels release glochidia that parasitize fish hosts to complete their development. After metamorphosis into juvenile mussels, they detach and settle to the substrate, where they grow into adults.

Distribution and ecology: They inhabit rivers, streams, and lakes with clean, well-oxygenated water across much of Europe and parts of Asia. Many populations are threatened by habitat loss, pollution, sedimentation, dam construction, and invasive species such as zebra mussels. Some species are legally protected in various jurisdictions.

Taxonomy and conservation: The name Unio has historically been used for a broad group of European freshwater mussels, but modern classification has moved some species to other genera. Conservation efforts include habitat restoration, water quality improvements, and monitoring of threatened populations to prevent further declines.