All About the Snail Shell: Answering Your Most-Asked Questions

Snail shells

If you’ve ever wondered what a snail shell is made of, or how those slithering critters make their hard-armor homes, you’ve come to the right place. I’m answering your burning snail shell questions – and some of the answers might just surprise you!

Let’s spiral right in…

Snail Shell Infographic

Why Do Snails Have Shells?

Snails have shells for a mixture of reasons.

Firstly, shells offer protection from predatory animal attacks. It also prevents their soft, moist organs inside the humped visceral mass from becoming damaged or drying out. And it provides a place for the snail to store calcium and other proteins and compounds.

Marine snails also use their shells to help protect them against waves, tidal debris, and rough sands.

Other animals (especially predators of snails) have a hard skeleton with ribs present, or a backbone-oriented structure, which offers speed, agility, and a number of other benefits when faced with a predator. Snails have none of those things. Instead, they have a shell.

We’ve got to let them have something, right?

Snail shells

What is a Snail’s Shell Made Of?

A snail’s shell, also known as its exoskeleton, is made up of several layers. Three layers to be exact.

Snail shells are predominantly made of calcium carbonate, and this is the middle of the three layers. The mineral is precipitated into conchiolin (also called conchins), which is relatively crack-proof and flexible but, of course, can still be broken.

The layer of calcium forms on top of a layer of ‘mother of Pearl’ or nacre. This layer is the one that touches the snail’s body (foot).

The layer you can see (the shell is covered by a sort-of shiny one), is the snail’s version of skin. It is known as periostracum, and it is the protective layer. It forms around the shell and protects it from external forces, such as waves and rocks, and corrosion that would otherwise negatively affect it.

How Do Snails Get Their Shells?

The growth of the shell matches the growth animal. The snail and the shell start out tiny and soft, right when it is just born or hatched from an egg. They do not change shells.

The shell that develops right before hatching is called a protoconch – it is a literal prototype for what is to come for the snail.

Egg-borne gastropods will eat their eggs to absorb any leftover calcium. They’ll need this to harden and build their shells.

As the snail grows bigger, the shell will harden and get bigger, too. This is due to a process called mineralization, and snails require steady source of calcium for this reason.

It’s just the same as one of our limbs — our legs and arms grow proportionally to the rest of our bodies.

Different snail shells

Why is a Snail Shell Spiral Shaped?

There are a few theories, but it is thought that snails have shells that are spiral in shape because they secrete calcium and other proteins from the mantle more on one side than on the other.

The shape likely works as a space-saving benefit, too, allowing gastropods to coil its entire body into a relatively small shell. It is also thought to be a way for them to be able to reproduce.

As you can clearly see in the above photo I took, snail shells have many different sizes and shapes, like the black devil snail, the black military helmet snail, trochus snail, spiny star astraea snail and others.

Can a Snail Leave Its Shell?

No, a snail can’t leave its shell.

Snails do not turn into slugs, simply abandoning the shell somewhere. Somewhere in evolution, the two animals broken apart in terms of gene pool. You can learn more about the differences between snails and slugs right here: Slug vs Snail: What’s the REAL Difference?

Leaving the shell results in almost certain death for gastropods, so they certainly wouldn’t wander off and leave their homes behind deliberately. The shell is an actual part of the snail’s body. It is attached! A snail would be incredibly vulnerable to predators without it.

Can a Snail Survive a Broken Shell?

Yes, a snail can survive minor breaks and damage to the shell.

Minor damage can be treated with compounds and different types of protein that the snail secretes from an organ called the mantle to build the shell as it grows. Rather than being in growth mode, however, the snail will be in repair mode.

Major damage isn’t so easily treated by this organism, though. If the shell is severely broken, it is more than likely that the snail will die.

What is Inside a Snail Shell?

The body of the snail, also known as the foot, is inside the snail shell! (Unless the shell is empty.)

Opened snail shell

Do Snails Abandon Their Own Shells?

No, not one gastropod species will abandon their shells. There are a few reasons why a snail shell might be empty, though. These include:

  • Death by natural causes

  • Predatory attack

  • Illness

Either way, when a snail has left the shell, the outcome is inevitably death. A snail cannot survive without the calcium carbonate home on its back.

Do Land Snails Shells Decay?

Yes, land snail shells do decay. They are made of calcium carbonate and other minerals and compounds, which are dissolved by rain and other environmental factors.

One study indicated that a snail’s shell would decompose/decay at a rate of around 6.4% annually. If the shell was broken, it rose to just over 10% annually. Dry habitats slowed down the rate considerably. The size of the snail shell also, obviously, played a big part. A giant African land snail would take longer to decay than a much smaller nerite snails.

Inside of a snail shell

Do Snail Shells Have Nerves?

No, a snail shell does not have nerves.

Unlike the shells of turtles, which have both blood vessels and nerves, snail shells do not have either of them.

Despite this, mollusks are still said to feel pain, or at least some sort of physical discomfort. Studies on various species have shown very clear avoidance responses when painful acts are performed on snail shells.

True or False: Snails Can Be Left-Handed!

It is true!

Land snails, sea snails (like Nassarius snails), and freshwater snails can be the equivalent of being right and left-handed in humans. (Which team are you – right or left side?)

Most gastropods are right-handed, with shells that coil in a clockwise direction. These are called dextral shells.

Very few snails are left-handed, with shells that coil in a counter clockwise direction. These are known as sinistral shells.

According to some reports, only 2% of great pond snails have left-handed characteristics, with shells that spiral counter clockwise.

At least 90% of all snail shells are believed to be dextral or clockwise. Sinistral shells are thought to be an anomaly, due to a genetic malfunction or mutation. The gene is thought to be passed down through female (mother/maternal) mollusks only.

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