This aquatic bivalve mollusc is a large species of freshwater mussel. The shell is thin but large (approximately 10 to 14cm when adult) and rather flat, even at the umbo. The shell colour is often pale greenish or brownish. Younger specimens can be difficult to tell apart from Duck Mussels.

Indicator Species - Leicestershire, Leicester & Rutland Local Nature Recovery Strategy.

Several of the large freshwater mussels look similar and can be easily confused, particularly with smaller specimens. The Duck Mussel, Anadonta anatina, is the closest in size and shape, but this has a dorsal margin that slopes over the hinge, whereas the Swan Mussel, Anadonta cygnea, is generally flat over the hinge giving it a rectangular look.

The two can also be distinguished by looking at the posterior (pointed end) adductor muscle scar. In the Swan Mussel, the scar is joined to the pedal retractor scar by a narrow isthmus, whereas in the Duck Mussel these two scars are completely merged.

Unless identified by a recognised expert, photographic evidence is required. A photo of the adductor scar is often needed. Note the shell's size. If it is an empty shell, it is advisable to retain this in case further checks are needed.

Rivers and lakes.

All year round.

Widespread and quite common in England, although there seem to be less records from elsewhere in Britain.

Fairly frequent in Leicestershire and Rutland