European fingernail clam
Sphaerium corneum
The European fingernail clam is a small freshwater bivalve, reaching up to 15 mm in size, with a characteristic rounded, almost spherical shell. It inhabits standing and slow-moving waters with muddy or sandy substrates throughout Europe and Northern Asia. Shell coloration varies from yellowish-brown to grayish-green, often featuring fine concentric growth lines. As a highly adaptable species, it plays a significant role in the nutrient cycling of aquatic ecosystems.
Details
Identification
Spherical to oval shell, umbo located nearly centrally, surface finely striated, shell margin smooth, color usually horn-colored to brownish.
Social behavior
Often lives in high population densities within the sediment, but does not exhibit complex social behavior.
Diet
Filter feeder; feeds on organic detritus, phytoplankton, bacteria, and protozoa taken from the water column or the surface film of the sediment.
Spawning substrate
No external substrate; development of the young occurs in brood chambers within the gill lamellae (ovoviviparous).
Overwintering
Overwinters buried in the sediment; can survive short-term freezing of the water body or desiccation of the mud.
Ecology
Ecological role
Important primary consumer and link between pelagic and benthic zones; promotes gas exchange in the sediment through bioturbation.
Natural predators
Fish (e.g., carp, weather loach), waterfowl, predatory insect larvae (e.g., dragonfly larvae), and muskrats.
Competitor species
Other Sphaerium species as well as invasive mussels such as the zebra mussel (Dreissena polymorpha).
Ecosystem service
Water filtration and clarification, nutrient recycling, provision of biomass for higher trophic levels.
Threats
Habitat loss due to river engineering, excessive eutrophication, and chemical contamination of sediments.
Scientific profile
Profile
Distinguishing features
Characteristic is the centrally located umbo without a cap (unlike Musculium). The shell is evenly convex and more finely striated than in S. rivicola. The interior of the shell is usually bluish-white. The siphons are long and fused at the base.
Diet
Phytoplankton, bacteria, and fine organic detritus filtered from the water column or taken up from the sediment surface.
Reproduction
Simultaneous hermaphrodite; self-fertilization is possible. The species is ovoviviparous: fertilized eggs develop in brood pouches (marsupia) on the inner gill lamellae. Juveniles are released fully developed.
Role in food web
Primary consumer and important prey for benthivorous predators; link between pelagic and benthic zones.
Protection & threats
Main threats
River engineering, excessive eutrophication, habitat loss through drying of small water bodies, and chemical contamination (pesticides, heavy metals).
Conservation measures
Protection and restoration of standing and flowing waters, maintenance of riparian buffer strips for nutrient reduction, securing the water balance in small water bodies.