|Chromodoris by David Doubilet|
Friday, October 19, 2012
Sunday, October 14, 2012
|COA students census clams at Hadley Point|
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.
Friday, October 12, 2012
Having just finished my midterm check-in with the class on how the course is going, I’ve been reflecting on my teaching, particularly the lectures for invertebrate zoology. I like to think my lectures are content-rich and characterized by enthusiasm for the material and that the energy I bring serves as an invitation for students to engage more deeply with the class content. My speaking style has been influenced by many people, and I am amused to sometimes hear echoes of their voices coming through in my lectures. Sometimes channeling my inner Diver Ed is a very effective teaching tool. Vi Hart is someone else whose expertise and exuberance I greatly admire. I’ll never be able to match her speed of presentation, probably to my students’ relief. This post was really just an excuse to share these cool videos on hexaflexagons.
Monday, October 1, 2012
There are some really nice echinoderm videos out there, but this one featured at Deep Sea News is unique. The beginning of the video is dramatic enough, with an advancing front of starfish creeping up a mussel-encrusted pier piling. Notice how fluid the starfish look in the time lapse. Mutable collagenous tissue doing its thing! Then the predation begins. The starfish’s stomach should look somewhat familiar if you’ve ever interrupted a feeding starfish. But seeing it from the perspective inside a mussel shell is a thrilling novelty. Not really a “mussel’s eye view” as they have no eyes, but still! As the stomach slides in, you can see the mussel’s gills, the ctenidia, on the right. The slender, ciliated filaments that make up the gill show up as blurry striations in the foreground. On the left is the mussel’s mantle, the organ that lays down the shell. The dark orange gonad can be seen extending into the mantle tissue. It’s all just starfish food.