Last week Arb Naturalists had the pleasure of walking Spring Creek in search of river mussels. If you've only ever encountered the sea dwelling mussels found on your local menu, you might consider taking to the rivers in search of these magnificent creatures. It might surprise you but these animals have some adaptations as innovative as some of our own.
For starters some mussels have what are known as "cardinal teeth." These structures are situated on the inside seam of each mussel's connected shells, and when a it closes up in fear of a predator the teeth interlock to prevent dexterous raccoons from rotating them open.
Some of the more interesting adaptations are involved in freshwater mussels' methods of reproduction. Since long distance migration would be difficult for the average bivalve, mussels disperse their young in the presence of fish. At this stage the microscopic young have a thin shell (sometimes with teeth) that can grasp and latch onto tissue. The goal for these little ones is to latch onto the gills of a fish, which will provide nutrients as they grow. The fish will also take them upstream or downstream to new waters. After about a month of maturation and travel they leave the fish and finish the maturation process burrowed in the sediment.
To help their young get from parent mussel to fish gill some mussels have to trick the fish. The Plain pocketbook mussel and the Fatmucket grow tissue near the shell edge that is fish shaped and has pigments resembling eyes that lure in real fish, and when they get just close enough, the mussel closes its shell and shoots its tiny offspring onto the fish.
Kidney shell mussels on the other hand start by growing mucus-encased sacks that look like grubs. They disperse these into the water, and when fish go to eat them the casing cracks open and out pour the tiny microscopic mussels. Already in the mouth of the fish they latch onto the nearby gills for a free ride.
Who would have guessed that such complex structures and peculiar behavior are hidden beneath those shells? Happy sand searching, and if you do go in search of mussels be sure to wear sandals and watch where you step. The Pink heel-splitter got it's name for a reason!
- Brandon Valle '14, for the Cole Student Naturalists
Photo of retired Biology Faculty Member, Gary Wagenbach.
Photo taken by Steve Braker.