freshwater mussel, swan mussel valves, anodonta cygnea, unionidae

swan mussel anodonta cygnea large species freshwater river aquatic bivalve valves mollusc unionidae shell thin elongated oval rather flat umbo pale greenish brownish growth lines grows inner lake piediluco terni umbria italy smell strong pungent fisherman bait daylight sunlight outdoor stony riverbed toilet shore winter internal filtration muddy bottoms siphon nacreous animal zoology organic filter nature natural