Naturespeak A naturalist's view of the world

August 18, 2012

Mussels Alive Alive, Oh

Filed under: Uncategorized — wykes @ 7:10 pm

It’s hard to get excited about an animal which looks about the same when alive as when dead. The public perception of clams and mussels has been tarnished by this fact over many years and these creatures rarely make it into the limelight.  After all, it is considered good to “come out of one’s shell” and bad not to. Unfortunately a clam out of its shell is a dead clam (the first way to tell a dead from a live clam). Clams don’t flush like an exploding covey of quail when discovered, or take fin like a lunker trout tearing across a riffle. No, they just sit there and, if they are disturbed enough, simply “clam up” with one quick shutting motion. If they are dead, they don’t clam up (another way to tell the difference).

All of this is not to say that the perception is the reality. In fact, clams can be downright fascinating and even, dare I say it, ingenious. First of all, our clams are not actually clams at all. They are freshwater mussels – two shelled (bivalve) members of the mollusk clan.  Though limited in structural design, they display a wonderful array of shell design, pattern, size, and color and possess some of the best animal names ever. Where else can you see individuals named Pigtoe, Purple Heelsplitter, Three-horn Warty Back and Fat Mucket without going to a mafia convention?  And, I know this may be shocking, but they really do move.

You’ll never truly really appreciate any of this until you spend some time observing them (try doing that with a mafia gang and it could get you swimming with da fishes). The shallow waters of the River Raisin just north of the Telegraph Bridge offered just such an opportunity recently. Like I said earlier, these shellfish are not hard to approach once found and I found them close to the seawall lining the bank at that location.

The mussels of note were Wavy-rayed Lamp Mussels. True to nature, they were well embedded in the gravelly sediment with only the top third of their form exposed to the current. Because they are relatively immobile, their shells were covered with matted dark algae. They looked like the surrounding rocks for the most part. A set of pink “lips,” kissing the current as it were, were the only give-away. These opening, called siphons, are the in and out tubes for feeding and feces.

The forward opening is the incurrent siphon and it is the largest of the two. Edged with a fingerlike fringe and patterned with bold stripes, the incurrent siphon takes in food particles suspended in the water. The particles stick to the mucus covering and are conveyed to the internal mouth (not associated with the aforementioned fake lips).  The excurrent siphon blows out the filtered water and waste products. As you might imagine, the mussel usually tries to position itself so that the wastes are ejected downstream from the intake (in other words, never spit upwind).

The soft inner workings of a mussel are covered by a thin mantle of flesh. The mantle produces the hard shell which in turn protects the whole shebang. Wavy-rayed Lamp Mussels have an oval shell with a yellowish outer skin layer marked by darker ridges that follow the edge contour. These ridges are believed to be growth lines delineating the annual periods of growth (very much like those on a tree). The River Raisin Lamp mussels exhibited at least ten lines each and reflected a decade of living in the river – through periods of raisin and fall’n water (a local joke around here).

The Raisin River has been, in spite of its name, falling as of late due to the extended drought conditions. Some areas of the stream were getting too shallow for a mussel’s tastes.  I spotted one individual in the process of shifting his position downstream (don’t ask me how I know it was a male – trust me). It was attempting to haul shell over a rocky platform in the river bed. Extending a huge white foot from the parted shell, the mussel wedged the tip into a crevice, swelled the tip in order to anchor it into place, and then contracted its foot. This mussel muscle action acted to pull the shell forward.  I even have a video to show you this, but you must be patient while viewing it.

Patience pretty well sums up the life of a mussel and a mussel watcher. Perhaps this glimpse into the secret life of Lamp Mussels will shed some needed light on the subject (not a local joke around here yet, but perhaps it could become one!).


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