|COA students census clams at Hadley Point|
Sunday, October 14, 2012
Bivalves are busier than they look
The processes of respiration, feeding, and locomotion in bivalves all rely on the animal moving water through the mantle cavity. To burrow, bivalves rely on muscle action to squeeze the shells closed, which puts pressure on the blood sinuses in the visceral mass (body) and moves blood into the foot, causing it to extend. The closing shells also squirt water anteriorly out of the mantle cavity, helping to soften the sediments in front of the burrowing clam, easing their work. Ed Yong at Not Exactly Rocket Science has a great description of the burrowing process along with photos and links to videos. The water movement for feeding and respiration is more subtle, and it relies on the action of the cilia that cover the extensive ctenidia (gills) of most bivalves. Water is swept into the mantle cavity through a larger, ventral incurrent opening at the posterior of the animal. The oxygen-rich water, laden with food particles, moves anteriorly and dorsally across the ctenidia, which both capture food and extract oxygen from the water current. The cleared water then passes back posteriorly and out through a smaller dorsal excurrent opening. You can sometimes see this process in the lab by carefully marking the water near the incurrent opening using food coloring or milk. You can also visualize water flow through mussels, using the spiffy technique of Schlieren imaging.