Swan Mussel - Anodonta cygnea


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.

Similar Species

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.


Identification difficulty
Recording advice

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.

When to see it

All year round.

UK Status

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

VC55 Status

Fairly frequent in Leicestershire and Rutland

Leicestershire & Rutland Map


Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map

Species profile

Common names
Swan Mussel
Species group:
Slugs & Snails
Records on NatureSpot:
First record:
15/08/1981 (Nicholls, David)
Last record:
05/02/2024 (Nicholls, David)

Total records by month

% of records within its species group

10km squares with records

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