Butterfly (Ellipsaria lineolata)
Butterflies prefer large rivers and are often found embedded in sand or gravel. Host fish include freshwater drum (sheepshead) and green sunfish.
The smooth outer shell varies in color between yellow and brown. Some shells may have rays that are V-shape or irregular rectangular blotches. Older shells will have faint rays or no rays at all. The inner shell is white and may have rainbow coloration toward the end farthest from the area where the two halves meet. An outline of the entire shell is somewhat triangular (imagine an equal-sided triangle blown up, like a balloon). The end closest to where the two halves meet is rounded from top to bottom. The opposite end is somewhat pointed. The raised part of the top of the shell where the two halves meet is squeezed together and pointed towards the closest end. This part is located below the elastic part of the shell that holds the two halves together.
This mussel may be confused with the pigtoe and deertoe mussels.
The Butterfly mussel is considered threatened in Minnesota.