From what I experienced, they're mainly filter feeder and a neat addition to the hobbyist. They tend to burrow alot but when they're in a fixed position, they'll stick out their "tubes" and start siphoning the water. One clam can filter alot out of the water, let it floating particles, small debris, anything. They keep the water very clean. But being that they're able to filter so much, food source become an issue in the aquarium or for me anyways. But if you find them in the wild, say in creek beds and flowing rivers. You'll see how clear the water is. That's from the clams, that's how much they can filter. As for the species, I have no clue. Best of luck!
They look like a native freshwater mussel....more technically a unionid. Did you buy them or get them from a stream near by. It's hard to tell what species from the vid. It's origin will help to narrow down the possibilities.