swan mussel...freshwater shell...

The swan mussel, which can be 20 centimeters long and 12 years old, feeds through a filter system, driven by a number of strong muscles. The animal has a large, muscled foot, which is used to dig the body for about 70% into the soil, and then to pump water in through one opening, covered with fine cilia to manure rough material. The water passes through the stomach, where edible particles are filtered out, along the gills, eventually leaving a second siphon out of the body. Wastes leave the mussel via this same siphon.

The swan mussel has two very strong muscles, the adductors, with which the two shells are held together. When there is danger, the mussel can close the shell so strongly that it is almost impossible for a human to open the mussel without breaking the shell.

The eggs (the female can lay several millions) come out quickly, develop small shells after about five days and adopt a parasitic lifestyle. The shells have small teeth, with which the larvae attach themselves to passing fish, on whose mucus they will spend a month. After this month, the mussels will be released, and they will spend the rest of their lives as filter-feeding bottom dwellersThe swan mussel is very sensitive to water pollution. If the habitat of the swan mussel becomes polluted, a large part of the population often dies, since every mussel that is dead pollutes the water itself, and thus aggravates the situation.

Swan mussels are sometimes used as an "early warning" system for pollution; increased mortality rates and changes in behavior may indicate water pollution.(Dutch wikipedia)