Fragile ancylid
Ferrissia fragilis
The fragile ancylid is a small freshwater snail with a cap-shaped, non-spiral shell. It typically reaches a length of 2 to 4 millimeters and is often transparent or light brown in color. Originally native to North America, it has spread globally as an invasive species in aquariums and natural water bodies. It prefers stagnant or slow-moving waters with abundant aquatic vegetation and is known for its ability to survive dry periods by forming a septum within its shell.
Details
Identification
Thin, cap-shaped shell without whorls; apex slightly offset to the right and rear; shell often very fragile and translucent.
Social behavior
Solitary, but often occurs in large numbers on suitable substrates.
Diet
Grazes on biofilms, diatoms, and fine organic material from surfaces.
Spawning substrate
Undersides of aquatic plant leaves, stones, or plastic surfaces.
Overwintering
Overwinters in sediment or on plant remains; can survive desiccation by forming a septum.
Ecology
Ecological role
Primary consumer that controls algal growth and serves as prey for small predators.
Natural predators
Small fish, leeches, predatory insect larvae, and waterfowl.
Competitor species
Other limpets such as Acroloxus lacustris or juvenile Ancylus fluviatilis.
Ecosystem service
Supports nutrient cycling by breaking down periphyton.
Threats
Severe chemical pollution of water bodies and complete destruction of habitats.
Scientific profile
Profile
Distinguishing features
The apex is blunt and shifted to the right, distinguishing it from Ancylus fluviatilis and Acroloxus lacustris (both with apex to the left). The species can form a septum (septifer form) during dry periods. The shell is extremely thin, translucent, and shows fine radial striations at the apex.
Diet
Grazing on algal periphyton (especially diatoms), biofilms, and fine detritus from plant surfaces.
Reproduction
Hermaphroditic, with self-fertilization (autogamy) being very common. Eggs are laid in small, gelatinous capsules containing usually 1 to 3 eggs on solid substrate.
Role in food web
Primary consumer; converts benthic primary production into animal biomass and serves as prey for fish and invertebrates.
Protection & threats
Main threats
No significant threats known; the species is a successful neozoon with high dispersal potential.
Conservation measures
No conservation measures required; monitoring of further dispersal in European waters recommended.