What are bivalves? Bivalves are marine and freshwater mollusks that have bodies enclosed by a shell consisting of two hinged parts, like clams and mussels. Just because you're out of school, it doesn't mean you should stop learning. Yes, you can get a combo with just bivalves, if that's what your heart desires. And you can also order a dozen of our other popular bivalves known as oysters. Get it while you can!