Did you know that some specimens in the Section of Mollusks were collected more than 180 years ago? Our collection represents every continent and every ocean on Earth—marine, freshwater, and land.
mollusks
(Not So) Boring Clams
by Tim Pearce
Some clams, in the families Teredinidae and Pholadidae, bore holes in wood or rock that is immersed in seawater. We humans often think of wood and stone structures as relatively permanent, but these clams force us to challenge that idea. In fact, the wood-boring clams, known as ship worms, are a centuries-old scourge to shipping activities because they weaken wooden ships and pilings.
The wood-boring clams are highly modified from the clams that normally come to mind. Their shells are reduced to a pair of abrasive cutting tools at the end of a long, worm-like body. The clam twists the shells back and forth, breaking off chunks of wood as it burrows through the wood. The clam eats the wood, aided by symbiotic bacteria that digest the wood. As the clams burrow, they somehow seem to know when they are near another clam’s tunnel and they avoid breaking into it, but how they know is a puzzle.
Human efforts to prevent shipworms from destroying wooden ships and pilings included coatings containing tributyl tin (TBT). While paints containing TBT did protect against shipworm damage, the chemical was toxic and caused reproductive problems in aquatic organisms. In particular, TBT causes masculinization of female fish, snails, and other aquatic species. So, other methods to protect wood are now used instead.
Rock-boring clams also have shells adapted for abrasion at one end, but they differ from the ship worms because the shells of the rock-boring clams are not as reduced as in the ship worms, and the rock boring clams do not derive nutrition from the rock particles. As the clams bore into the rock, they grow, so the burrow tapers wider inward, so the clam shell cannot get out. However, the clam gains great protection from predators. The clam siphons protrude through the rock opening to bring in water and food and to expel wastes.
Other clams specialize in boring in calcium carbonate. These clams are important in the destruction of limestone, reefs made of coral skeletons, and even shells of other mollusks.
Timothy Pearce is the Head of the Section of Mollusks at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.
Section of Mollusks Tours
Did you know that the Section of Mollusks Assistant Curator Tim Pearce has been conducting monthly behind-the-scenes tours for the public since 2007?
On these tours, participants often learn for the first time that the museum has huge collections and scientists who conduct
research, and they see crowd pleasers such as the killer sea snail, the giant clam, and they look through the shell to see the beating heart of a live land snail.
Check our Section of Mollusks for tour times!
Ask a Scientist: Why are slugs so slimy?
Ask a Scientist: Why are slugs so slimy?
Assistant Curator and Malacologist Dr. Timothy Pearce explains why slugs are slimy and talks about the incredible and useful properties of slug slime.
Ask a Scientist is a new short video series where we ask our research staff questions about the millions of amazing objects and specimens stored in our collection. Tune in on YouTube, and submit your own questions via Twitter @CarnegieMNH.
Shopping cart symbol
by Patrick McShea
The shell-encrusted shopping cart in We Are Nature would get lots of visitor attention even if it weren’t suspended from the ceiling. Hundreds of zebra mussels coat the familiar contraption, creating an eerily appropriate symbol for human-altered natural systems: An empty icon of consumer culture armored by hitchhiking organisms of global trade.
Zebra mussels, a freshwater species native to the Caspian Sea and Black Sea, were unwittingly introduced into the Great Lakes during the 1980s via ballast water dumped by ocean-crossing cargo ships. The creature’s rapid dispersal since then has been attributed to the passive drifting of tiny larvae and the ability of mature zebra mussels to attach to boats moving between the lakes and adjacent river systems.
As invaders, zebra mussels have profound effects on ecosystems. They feed by filtering tiny organisms from the water, and by sheer numbers can out-compete fish larvae and native mussel species dependent on the same food source. Zebra mussels attach to any submerged hard surface. Their profusion attracts attention when it results in clogged water in-take pipes, but not necessarily when thousands of the striped fingernail-sized creatures occupy physical positions atop existing beds of native freshwater mussels.
At Carnegie Museum of Natural History, concern for the health of our region’s diverse population of native freshwater mussels has a long history. In 1909, Arnold Ortmann, then Curator of Invertebrate Zoology, termed the disappearance of mussel species “the first sign of pollution of a dangerous character in a stream.” His observation was based upon biological surveys in rivers and streams throughout Western Pennsylvania, fieldwork performed during a time of rapid industrialization that garnered the museum an irreplaceable collection of local mussel shells.
Patrick McShea works in the Education and Visitor Experience department of Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences of working at the museum.
How Scallop Eyes Relate to Human Uniqueness
by Timothy A. Pearce
We humans like to think we are special among all creatures. To support that notion, we claim unique traits such as language, tool use, consciousness, etc. Oops, all of those traits have now been shown to occur in other species. Do not fear, though, for I have found a trait that seems to be unique to humans: a fondness for 90 degree angles (aka right angles). You heard it here first! I don’t know where on the evolutionary lineage to modern humans we acquired this fondness for right angles, but evidence of this fondness is all around us in the modern built environment.
What does fondness for right angles have to do with scallop eyes? First let me tell you about the amazing eyes of scallops. They have up to 200 eyes along the mantle margin, and those eyes contain concave mirrors. Instead of being similar to cameras (as our, and most, eyes are), scallop eyes are similar to reflecting telescopes, and each eye has two retinas so they can see clearly in both narrow and peripheral views at the same time.
New research published this week in Science (and described in the New York Times ) demonstrates that the concave mirror of each scallop eye is tiled with more than 100,000 square mirror tiles. Did you get that? They are squares! Outside of the human built environment, right angles are scarce. So to find squares in the eyes of scallops is remarkable. The properties of the tiles making up the mirror has implications for the scallop’s ability to see in the particular wavelengths of light in its surroundings and can inspire improved human optical devices. Future studies will have to examine why a scallop needs to have such amazing vision. But for now, I am amazed to know that scallop eyes contain square mirrors.
Timothy A. Pearce, PhD, is the head of the mollusks section at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.
