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For most of us, we’ve seen conch shells of very small or very large sizes at some point in our lives, whether this is at the beach or in a gift shop near the shore. Simply being a “seashell” to many, a lot of folks neglect to realize that these shells are homes to mollusks that live inside of them for periods of time. We may not see any significant or rapid changes in these shells during our brief encounters with them, but you may be wondering how exactly there are such wide variations in shell sizes for these neat-looking husks.
So, do conch shells grow?
Yes, they very much do. A conch shell doesn’t grow on its own, though—it’s a direct result of the residing animal’s activities. A conch shell’s shape and size are the byproducts of food waste excretions from the animal inside.
A conch shell is beautiful in its appearance with its classic spire at the top and subsequent side opening. It’s inside of this opening where a mollusk—a type of sea snail—lives, and it’s an impressive piece of natural engineering.
What is a Conch Shell?
A conch shell is the exoskeleton of a particular type of mollusk, called a conch (pronounced like “conk”). There are three layers comprised of calcium carbonate with about 2% protein present. These layers are not made up of any living cells; they are simply the product of the animal’s excretion of minerals and proteins that deposit onto the shell.
How and Why Do Conch Shells Grow?
There is a specific and particular way that a conch shell grows. The mantle tissue of the snail—the part that rests underneath and in direct contact with the shell—provides the minerals and proteins which cause the shell to grow. Conches never shed their exoskeletons, so they instead enlarge to accommodate the mollusk’s growth.
The conch shell is an extraordinary piece of engineering from the sea. If you have ever been fortunate enough to handle a conch shell, you quickly notice how strong and durable they are—they’re nearly impossible to break, chip, or crack. This is due to the bone-like structure created by the calcium carbonate deposited through excretion into the shell.
Their Diet Makes the Shell Grow
Conches have a robust diet of eating an abundance of things like algae, sea grass, and other dead plant materials. The mollusk digests the food through their mantle and deposits it directly into their shell. They also push the shell outward from the inside to make it larger as they mature.
This activity provides for the growth and development of three distinct shell layers: an outermost uncalcified layer, a central calcified layer, and an inner calcified layer.
Outermost Uncalcified Layer
Sitting on the outermost surface of a conch shell is an uncalcified layer called the “proteinaceous periosteum.” It consists of a hard yet thin layer of protein to protect the shell as it grows. This accumulates calcium ions which promote crystallization.
Central Calcified Layer
The first more outward calcified layer, known as the prismatic layer, creates the center part of the shell. A hard, prism-like form of calcium carbonate makes up its composition. This gives off a chalky appearance, further promoted by the proteins deposited by the animal from its mantle.
Innermost Calcified Layer
The last and inner calcified layer—otherwise named the “nacre”—is the pearly layer covering the prismatic layer, and it seals all of the layers together to create an unusual protective barrier. It’s a pearlescent lamellar substance formed by the epithelial cells from the mantle’s surface.
A brick-like arrangement creates this nacre layer, and it is amazingly strong. Most people might recognize it what’s referred to as “Mother of Pearl.” These block structures interfuse with biopolymers along with calcium carbonate sheets, giving the shells their resistance, resilience, and elasticity.
What Does a Conch Shell Look Like Once Mature?
A conch will reach maturity around four years old, but the shell continues growing so long as the snail inside of it is alive. Its appearance doesn’t change nor does the shape become altered; only the size of the shell gets bigger as the animal ages. The shell also remains intact throughout the conch’s entire life.
When a conch reaches maturity, its shell will end up in a spiral shape. Depending on the species and any other influences on its growth pattern, this can go in either a left- or right-swirling direction. If it spirals right, it’s considered “dextral; if it spirals left, it is considered sinistral.
Shape and Size of a Conch Shell
Conch shells have long, central spires—or eye stalks—with a narrow and long opening that flares out along with a siphonal canal. This canal comes with an indentation at the anterior area of the shell, also named the “stromboid notch.” The spiral pattern of these shells develops throughout the conchs’ lives, complete with bumps to make room for and accommodate growth.
Conch shells also have a foot-like structure with a moon-shaped, yet horn-like and pointy, operculum. The flared lip on the shell opens in an outward direction upon reaching sexual maturity.
So, when you see a very large conch shell lying on the beach, you can assume with a fair amount of certainty that the snail was very old when it died. You’ll know a conch died young when you see just a small shell.
What is the Purpose for the Growth of a Conch Shell?
Not only will the development and growth of the conch’s shell increase to accommodate the life living and growing inside of it, but it serves a host of other purposes as well. The highly styled engineering of the shell gives the mollusk everything it needs to remain safeguarded from anything that could possibly hurt it.
The shell protects the mollusk, providing a hiding place in case of danger. It also provides shelter from cold weather, super-hot sun, and other weather or sea conditions that could prove to be harmful.
People will sometimes cut off the tip of the spire to create a horn as well. For centuries, people used them for communication and announcements.
How Much Does a Conch Shell Grow Each Year?
The rate of a conch’s shell growth will depend upon the species of conch as well as how well it eats. Therefore, it’s entirely dependent upon the individual.
Conch shells grow continuously. They don’t stop and start back up again like a human child’s growth does. Because these shells function as a way for conchs to deposit waste, they shape and grow all day, every day.
Conch shells have a definite pattern and method of growth. There is no cell division and regeneration as with skin; rather, their growth is due to a buildup of proteins and calcium carbonate that the animal secretes over the course of its life. Conch shells provide conchs with a strong, durable structure while keeping them safe from predators and inclement elements.
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