Mollusks For Kids I: Clams, Mussels, and Oysters
As we approach the summer months, I start anticipating meals with mollusks on the menu. Perhaps you too enjoy consuming clams, mussels, scallops, and oysters. I am lucky enough to spend time during the summer in an area where I not only get to cook and eat shellfish, but also collect them.
Perhaps you avoid shellfish and do not enjoy cooking or dining on it. Regardless of your eating preferences, take advantage of relatively easy access to mollusks, making them available to stimulate your child’s curiosity.
Species in the phylum Mollusca or mollusks, in general, make up 23% of marine organisms, so they represent an important number of sea creatures one can learn about. There are about 85,000 to 100,000 species of mollusks that are divided into several different diverse classes including snails (both marine and terrestrial), squids, octopi as well as around 15,000 species of clams, mussels, and oysters. For our purposes here we’ll focus on the class that includes the clams, mussels, and oysters that are common in our harbors, estuaries, lakes, on our beaches, as well as in our pots and on our plates. This class of mollusks is known as bivalves (Bivalvia).
If you live by or visit the seashore, plan an outing during which your child can collect marine mussels or dig for clams at low tide. If you have access to a freshwater lake or river with clams or mussels, help your child identify where they are and encourage her to collect some.
Even if you do not live by the seashore, clams, mussels, and oysters are available in many supermarkets for purchase. Scallops, which are part of the clam family, are also available for purchase. However, you are buying only the adductor muscle or the muscle that the animal uses to open and close its two shells or valves to swim. It is rare that you will have the option to buy the entire scallop with its shell or other body parts, thus making examining them an incomplete experience.
Collect or purchase a couple of clams and mussels and explore these creatures at home and in your kitchen. (Most of what will be available for purchase will be saltwater or marine species). Oysters tend to be a little more expensive but add one to the mix for a complete mollusk investigation.
Ideally, your child will have an opportunity to dig for clams or collect mussels at low tide. Digging for clams? How can you tell where to dig? What are you looking for? How deep is the clam or how far down do you have to go to find one? This is a messy but super fun thing for kids to do as it is very sensory experience and there is a tremendous feeling of success in finding a clam.
If mussels are available for collecting, describe where they are. Are they alone or in clumps? How are they attached to the rocks or each other and what holds them together (they are attached with something like a string or thick thread called a byssal)? Are the shells a variety of colors or the same? Are they the similar or different sizes?
Rather than just grabbing the mussels, ask your child to describe what he sees and feels.
As noted above, if you can not collect them, these shellfish varieties are available for purchase at various grocery stores, so buy a few take them home and let the examination process commence. Several different kinds of clams may be available, or cherry stones, quahogs, steamers, razor, or Manila. Oysters, from different parts of the country, come in a variety of sizes and shapes. You do not have to purchase all the different varieties if they are available, but perhaps your child can see the options and choose.
Begin by examining the shell or shells. A hand lens will be helpful for taking a closer look. Ask your child to:
- describe the color,
- find language for how the shell feels,
- and what it smells like.
- Does it make a noise?
- Tasting may have to wait until the shell is opened or after cooking.
How many shells are there (2, or why they are called bivalves)? What shape are they (oval, triangular, elongated oval)? A razor clam shell has an elongated shape (if you can’t purchase these, check out this photograph). Are the two shells similar?
Now open those shells. An adult will have to take responsibility for this, as it requires some strength and the use of sharp objects such as a knife. A flat-head screwdriver will work as well and is safer than a sharp knife – but be sure to clean it well first.
Never opened a clam or oyster? Here is a video explaining how: https://www.youtube.com/watch?v=Uy-rbEXFwLw
If you have trouble opening the shells raw, you can steam them for a short period, but this cooks the organism inside and changes its texture and color.
Remind your child that the class of mollusks you are observing are called bivalves. They are described as bivalves because they have two shells of roughly equal size that are held together by a hinge. Can your child find the hinge? What does it look like? What does it feel like? Encourage finding the language to describe this part of the animal.
Once open, your child can examine the animal inside. They may not be easy to see, but in general, these mollusks should have at least 2 identifiable body parts. The first is called a “visceral mass” that is essentially a sack of internal organs. Ask your child to think of other organisms that have legs, arms, fins, tails, or other identifiable body parts. Even insects have recognizable body sections (three of them).
The bodies of these mollusks are not segmented. Their bodies are soft or squishy. In fact, despite the fact that you may first recognize these animals for their shells, the term mollusk comes from the Latin word “molli” which means soft. Mollusks are invertebrates, so they have no spine or backbone. These animals have no bones or an exoskeleton such as you would find on a beetle. Their shells are basically self-grown protection for the soft animal living inside. What else is missing? They also have no hair!
The second recognizable body part is called a “foot.” The foot helps the animal move or to attach to something on the bottom so as to remain stationary and not be transported by the tides or currents. A clam’s foot, or siphon, helps propel it through the water or to burrow in the mud. They can take in water and squirt it out with enough force to move.
Watch this burrowing clam: https://www.youtube.com/watch?v=6JyNpPUj1ys
Can you find a muscle that is used to open and close the two shells?
Some mollusks have what is described as a head (think of a snail or octopus), but not the bivalves that we are examining here. Clams and mussels do not have heads so they do not have what else? You guessed it they don’t have brains!
They also do not have eyes, but they can detect changes in light. Scallops have rudimentary eyes (see photo below), but you will note that they do not look like anything we may think of as eyes.
How does your child think these animals eat? Well, without a mouth, there must be another way. But in this case, your child won’t be able to see anything that will help to figure out the answer to this question, so you will have to explain. Bivalves are filter feeders. This sounds like what it is, or sucking in water and filtering or straining out the organic particles, such as pieces of algae or phytoplankton, that provide the nutrients the animal needs to live. The filtered nutrients are then funneled into their mouths.
That water that is taken in also has oxygen in it that passes over gills. Like fish, these bivalves do not breathe but extract oxygen from the water with their gills allowing them to survive underwater.
The mantle is an organ that combines the elements calcium, carbon, and oxygen and then excretes crystalline calcium carbonate to make the animal’s shell. Again, you may not be able to determine which part of the squishy thing you are looking at is the mantle, but if you get a question about how the shell is created, you have an answer.
All of the mollusks we have discussed can make pearls, but there is a special oyster that produces the pearls we associate with expensive jewelry.
Pearls are produced when something gets inside the shell and irritates its occupant. A grain of sand, for example, can enter the shell and rub against the visceral mass. This can be more than irritating and maybe even painful, so the organism excretes the same material around the grain of sand that it uses to coat the inside of the shell. That material is called “nacre.” The nacre covers the irritant reducing discomfort while also creating something beautiful. A pearl can take 3 – 6 years to form. These days most of the pearls sold for jewelry are grown, or people purposely introduce the irritant into the oyster. Natural pearls are rare.
Compare and Contrast
If you have several clams, mussels of oysters, what differences does your child notice among them? Are the shells different sizes, colors, or shapes? What does your child notice about differences between mussels, clams, and oysters? The color of the shell is an obvious choice. What other distinctions are easily identifiable? If you do not want to purchase them, you could do these comparisons while standing at the fish counter.
Clams, mussels, and oysters live in different places. Can your child tell where the animal lives based on characteristics of its shell? Clams prefer to bury themselves in mud. Mussels and oysters attach themselves to rocks, anchors, or docks. Scallops live on the sea floor, but they “swim” around rather than remain buried or attached to something. The term “swim” is used here loosely. See this video and talk about whether the term “swim” is appropriate. Is there another term your child can think of that would be more descriptive of how scallops get around?
Different species of clams and mussels can be found in fresh and salt water. Your child may have observed only those animals from one of these habitats. Perhaps you can find photographs of the same animal, either a clam or mussel that resides in the other or different ecosystem. So if you examined animals from marine environments, find photographs of their freshwater relatives. The fresh and saltwater varieties are not very closely related, despite bearing the same names. Scallops do not live in freshwater and are only found in saltwater marine environments.
Compare predators. The fresh and saltwater varieties of clams and mussels are on the menus for different animals. Who eats clams and mussels at the seashore? Horseshoe crabs, starfish, whelks, crabs, and seagulls eat saltwater clams and mussels. Even some large marine mammals like walruses include mollusks as a major part of their diet. Their prominent tusks serve to dig around in the mud, Freshwater clams and mussels are a food enjoyed by several mammals, such as otters and raccoons.
Once the shells of the different animals have been opened, compare what is found inside. Is a raw oyster the same color as a raw clam or mussel? What differences can your child see among these animals?
Compare clams and mussels to other mollusks. You will most likely need photographs to make these comparisons. One group of mollusks is referred to as Gastropods and includes snails and slugs. Gastropod means “stomach-foot” since this is literally how they move around.
Alternatively, introduce your child to those mollusks whose shells we often collect such as conch or cowry. If you are lucky enough to live somewhere with a Museum of Natural History then check out their shell collection and be prepared to be amazed how creative nature can be. Bivalves and their other relatives in the phylum Mollusca can get quite showy.
Store bought clams and mussels may be more uniform in size than those collected at the seashore. Nevertheless, invite your child to make this determination by measuring their length and comparing those data. Are the clams or mussels being measured the same size? How big is the biggest one? How small is the smallest?
On a scale, weigh a clam or mussel before it is opened or shucked. After it is opened, weigh what is found inside. How much do the shells weigh versus the body of the animal inside?
Some clams can live to be 150 years! How many more years would you have to live to match their life span?
Dissect a clam or mussel. Can you distinguish any internal organs such as a heart, kidney or stomach? The stomachs are often easy to identify. The other body parts may be harder to distinguish but worth taking a look at.
Clams can be eaten raw, steamed, smoked, baked, fried, grilled, or in soups, such as a chowder. At home or when eating out try different recipes including these shellfish. Which one does your child like best? Ask friends and relatives what their favorite way to cook and eat clams is. Keep track of those responses and find a way to represent them visually such as by creating a chart.
The study of mollusks is called malacology.
Increasingly, much of the shellfish we consume is now being farmed. Do you have any aquaculture in your area that you can point out?
Sometimes shellfish may not be available for eating. Bivalves filter water for oxygen and nutrients, but in doing so they may also collect toxins like bacteria on their filters. If we consume these toxins they can make us ill.
This may sound like a subject to avoid as it can make eating shellfish seem hazardous. However, in this discussion are some fascinating lessons about animals in their ecosystems. Bacteria or algal blooms exist in many marine environments. We most often think of these toxins as doing direct harm to the animal that consumed them, but in some cases,it is only higher up in the food chain that the toxin affects well-being. So the clam can flush the toxin on its filter and remain unharmed. However, if we eat that clam before it has had a chance to clean its filter, we will feel the consequences.
Relatedly, several groups are working to reintroduce oysters into ecosystems because they are very good at cleaning up pollutants AND they may keep beaches or land from eroding. Perhaps there is a group in your area who is doing this work and you can your child could visit with them.
Here is an example of a program in the Chesapeake Bay. http://www.chesapeakebay.net/issues/issue/oysters
What does it mean to “be happy as a clam at high tide?” (It means you are snug and extremely happy).