Now that’s an old clam!

Well, I’ve written about animals that live a long time, and I’ve written about clams. So I guess now would be a good time for an entry on clams that live a really long time!

Scientists at Bangor University in the United Kingdom have found a quahog clam that holds the title of oldest animal in the world – at a whopping 405 years. Now that’s old.

So what are quahogs? Quahogs (pronounced “KO-hogs”) are hard shell clams. If you picture a clam on the menu in a seafood restaurant, you’re thinking of a quahog. They, along with soft-shell clams, oysters, scallops and mussels, are known as bivalve mollusks. That’s because their shelves are made of two halves, or valves. The valves connect at a joint called the hinge, which contains the oldest part of the clam’s shell. That part is known as the beak. The hinge will be in an open position and the valves ajar if possible, but if water conditions are bad or there are predators around, the clam can snap its valves shut, and hold itself tightly closed for as long as necessary.

Quahogs have several muscles that are important for their physiology. Their adductor muscles control the opening and closing of the hinge. They also have a foot for burrowing in the sand, which is controlled by the foot retractor muscles. One other important feature of their bodies is their necks. A quahog’s neck can stick upwards through the sediment and into the water above. Through the incurrent siphons in their necks, they filter water over their gills, collecting algae, plankton and diatoms to eat. The filtered water then gets spit back out through their excurrent siphons.

There are actually 2 different species of quahogs in the world. The clam that we eat in North America is called Mercenaria mercenaria. These clams are also known as Northern quahogs, round clams, chowder clams, littlenecks, topnecks and cherrystones. You might wonder at their scientific name, which is related to the Latin word for money (“mercenaria” means “something of value”). Apparently, Native American tribes in New England used to use quahog shells to make valuable beads for barter. In addition to the Northern quahog, however, there is another species native to the North Atlantic ocean. This species is called Arctica islandica, and it is this variety of quahog that was found to be over 400 years old. It was collected from water over 250 feet deep off the coast of Iceland, and it beats the previous record holder for longest-lived clam by several decades.

So how do the scientists know how old these clams are? Remember, the oldest part of the clam’s shell is the beak, which is found near the hinge. Every year a quahog is alive, its shell grows outwards from its beak. And every year, the growth creates a ring in the shell. Scientists can simply count the number of rings to see how many years of growth the shell has undergone. This is very similar to the way that trees are dated.

How do these clams live so long? No one really knows, though the finders of this old quahog speculate that it may be due to slow cell division. Scientists think that geoducks, another kind of clam, can live 100+ years because they have a low-stress lifestyle (you can read my entry “What do you call that?” if you missed it before). So an alternate theory could be that perhaps quahogs in the waters off Iceland live even easier lives than geoducks in the Puget Sound!

I don’t know if the same could be said for the North American quahog, though. There is a large and active clamming industry in American and Canada, which harvests quahogs for consumption around the world. So it’s a safe bet that they do not live as long as their Icelandic cousins.

You can find an article describing this clam on National Geographic Online:
http://news.nationalgeographic.com/news/2007/10/071029-oldest-clam.html.