When people think of a bivalve organism, they should typically imagine a sessile animal with it’s shell partially or fully buried in the sand and feeding through its elongated siphon which filters out plankton in the water column.
A scallop, the only migratory bivalve organism, seems to defy many stereotypical morphological features that are endemic to the class Bivalvia.
Obviously since they are not sessile, they have had no need to develop a way to anchor themselves in one spot. Infaunal bivalves such as clams, have developed a foot that elongates and helps them bury themselves in soft substratum. Similarly, epifaunal bivalves such as mussels have developed byssal threads that hold them in place. Because scallops have no need for these mechanisms, its lifestyle differs from your typical bivalve.
After watching everyone torture the poor Spiny Pink Scallops (Chlamys rubida) in the sea tables in lab 3 yesterday, I became fascinated by the way they are able to swim.
I did find a couple interesting papers about scallop swimming dynamics.
This first one is an interesting study on scallop body size and how it effects swimming trajectory in different flow speeds. They found that in higher flows smaller scallops always had a backwards net swimming trajectory in both their active swimming period and passive sinking period. Larger scallops made more progress in their active swimming period but were still at the mercy of the current in their passive sinking period. These results are fairly predictable but it’s cool to see swimming dynamics rigorously quantified.
This is a study on the effects of barnacle encrustation on scallop swimming dynamics. They found that barnacle encrustation negatively effects active swimming efficiency in both height and distance. Also they found that scallops encrusted with barnacles required more energy to swim a given distance. In the energetics studies they did, they found that there was no detectable difference in aerobic energy, but there was a difference in anaerobic energy required. Basically, they respired the same amount of oxygen, but more anaerobic nutrients were required by the barnacle encrusted scallops.
Another interesting (and relevant to our class!) thing I found in this paper is that while barnacle encrustation decreases the drag coefficient (Cd), sponge encrustation does not change it very much. So when our Chlamys rubida were frantically evading the Pychnopodia, the encrusting sponge should not have been making a very bid difference in drag.
Hoorah! Go Scallops!