Hydrobiidae

Hydrobiidae is a family of minute freshwater snails with an operculum, belonging to the class Gastropoda. Members are part of the Rissooidea (in some classifications Truncatelloidea). The group is diverse and widely distributed, with many described species and many more likely undiscovered. They occur in freshwater and brackish water, particularly in springs, streams, rivers, groundwater, and subterranean habitats such as caves. The highest levels of endemism are associated with isolated springs and groundwater systems, making many hydrobiids highly restricted in distribution.

Shells are typically very small, often less than 5 mm in height, and range from elongate-conical to nearly spherical. The aperture is usually round to oval, and the outer lip is often narrow. The shell surface displays a variety of sculptural patterns depending on genus, but many species have smooth to softly ribbed shells. The operculum is corneous and paucispiral.

Ecology and biology: Hydrobiids graze on biofilm and algae on submerged surfaces; some genera are adapted to subterranean life, including subterranean streams and caves. Reproductive biology is variable and incompletely documented across the family; many species have not been well studied.

Taxonomy and conservation: Hydrobiidae has undergone extensive revision, with many genera moved to or from the family as molecular data reshape higher-level gastropod classification. As a result, the circumscription of hydrobiids is not uniform across sources. Habitat destruction, groundwater extraction, pollution, and the introduction of competing or predatory species threaten many hydrobiid endemics, leading to conservation concerns in several regions.