order UNIONOIDA: 1020 Recent species.
2 genera, 1 family, 5 superfamilies
These are the freshwater mussels. There are six modern families, restricted entirely to fresh waters. In addition, there are several fossil families.

order ADAPEDONTA: 17 Recent species.
1 superfamily

order ARCOIDA: 5 Recent species.
1 superfamily
Arcoids are primarily marine. However, one family is represented in fresh waters.

order CARDIOIDA: 48 Recent species.
3 superfamilies
Cardioids are mostly marine, with a minor radition into freshened waters.

order LUCINOIDA: 16 Recent species.
1 superfamily

order MYOIDA: 53 Recent species.
3 superfamilies
Myoids are also primarily marine bivalves, but there are freshwater species as well, including species of the Dreissenidae.

order MYTILOIDA: 38 Recent species.
1 superfamily
There are a few secondarily freshwater species in this order, but otherwise mytiloids are primarily marine.

order SPHAERIOIDA: 272 Recent species.
1 superfamily
The Sphaeriidae is the second-most species-rich radition of bivalves into inland habitats.

order TRIGONIOIDA: 8 Recent species.
2 superfamilies
Trigonioids are the marine sister-group to freshwater mussels.

order VENEROIDA: 162 Recent species.
5 superfamilies
The Cyrenidae represents the most significant radition of veneroids into fresh waters, but there are also a number of freshwater species in primarily marine families.

order ARCHANODONTIDAE: fossil only.
2 genera

order MODIOMORPHOIDA: fossil only.
1 superfamily

order PECTINOIDA: fossil only.
1 superfamily
An order of bivalves that has freshwater species or at least species attributed to freshwater clades.

order PTERIOIDA: fossil only.
1 superfamily
There are not really any freshwater pterioids, but at least one fossil family has been assigned to a freshwater clade.