Who needs a head, two feet, and a spine? Not a freshwater bivalve. These small, headless critters have an enormous impact as water filters in a river’s ecosystem. Their bodies clean algae, silt, and heavy metal out of eight to 10 gallons of river water daily.

Mollusks are a big group of animals that have soft bodies inside shells. Bivalves are a smaller group of mollusks. Some living bivalves include scallops, oysters, clams, and mussels. Most live in salt water, but a few kinds of mussels live in fresh water.

On the outside, bivalves look like two seashells stuck together. Their flat, squishy bodies are protected by a hard shell. The shell’s two parts are called valves. They’re attached by a sturdy hinge. Strong muscles hold the valves closed. Bivalves are usually symmetrical. Look closely! If a bivalve is split, it looks the same on both halves.

A freshwater bivalve is a living mini water filter. It strains objects from the water. Most bivalves have two tubes called siphons. One is an entrance, like a front door. One is an exit, like a back door. The entrance sucks in water. The exit pushes water back out. Both siphons have a tiny hole. Big particles can’t flow through the siphon hole into the bivalve’s body. Small particles can. Inside, the particles get stuck on the body’s slimy gills. Next, they move to the mouth. Bits and pieces are digested by the gut. Anything that isn’t broken down goes back out the exit siphon.

Bivalves have many parts that other animals have: hearts, guts, gills, and a foot they use to bury themselves in sediment. What’s unusual about them is that they’re missing quite a few parts other animals have: heads, bones, and eyes. No nose? No problem. Bivalves have all the parts they need to do what they were created to do.