Surprising Snails of Singapore

Almost everyone knows what a snail looks like. The familiar land snails that we see, however, are the tip of the snail iceberg. Most snails are marine!

You are almost certain to see a snail on almost every shore. They are found on moist rocks and boulders, on mangrove trees and other hard surfaces near the sea. They also creep among the seagrasses, while small ones creep ON seagrasses and seaweeds. Others plough through the sand. Yet more specialise on plants and animals of the coral rubble area or reefs.

The snails that most of us are familiar with typically has a large muscular foot supporting a the rest of the body and internal organs. In most, the entire snail can be retracted into a protective shell.

Shells for life: A snail makes its own shell and stays in the same shell all its life. It does not moult its shell like a crab does. You can only remove a snail from its shell by killing it. All shells sold as souvenirs are obtained by harvesting living snails and killing them.

A shell is made mostly of calcium carbonate and shell material is added to both the outer edge as well as existing shell so that a shell gets both bigger and thicker with age.The snail's shell is secreted by a thin, specialised tissue called the mantle. Pigment cells in the mantle create the beautiful colours and patterns of the shell.

Here's some of the beautiful patterns found in some of our moon snails (Family Naticidae).The outer surface of a shell is usually covered with a tough protein layer. Some snails may have a layer of fine brown hair (called periostracum) on their shells. The Spiral melongena (Pugilina cochlidium) is commonly seen on our shores. When the snail is alive, its shell is covered with hairs that trap sediments and thus camouflages this large snail. When the snail dies, the shell is smooth and bright orange. A hermit crab usually moves in to use the empty shell.

Mobile home: The shell protects a snail from drying out as well as from predators. Shells come in a a wide range of shapes, textures and sizes. These tell us a lot about the way of life of the owner. Some have spikes to keep off predators or large lips to protect them as they forage for food. Others have pointed tips to protect the siphon (long tube-like body part).

Snail door: There's one problem with the shell, there's a big hole in it!

Most snails close the shell opening with an operculum (a hard 'door') attached to the foot. The operculum may be thick and tough to prevent crabs from getting a grip of the edge of the door and digging out the snail.

Nerites (Family Neritidae) (in the photo on the left) are commonly seen on our rocky shores. They have door with a lock! The operculum locks shut so that its more difficult for crabs to dig out the snail.In the Turban snail (Turbo bruneus) (in the photo on the right), the operculum is thick and rounded, also thwarting crabs who might try to pry out the snail.

In others, the operculum is thin and flexible so that the snail can withdraw deep within the coiling shell out of reach of crab claws. Like this Top shell snail (Monodontia labio) in the photo on the left. In some shells, the opening may be narrow and thickened so crabs can't stick their fat pincers in. As in the dove snails (Family Columbellidae) in the photo on the right.

The operculum may also be used for more than just shutting the door. In Conch snails (Family Strombidae), the operculum is shaped like a dagger and used like a pole-vault to hop along.From left to right are the beautiful large spider conch (Lambis lambis) and the smaller edible Gong-gong (Strombus canarium).

What happens when a snail dies? Empty shells are not wasted! They are vital to hermit crabs. We should NOT take home empty shells from the shore as we might be depriving a hermit crab of a home. Also, these shells eventually break down into calcium that baby snails need to make their new homes.

Here's a group of the Striped hermit crabs (Clibanarius sp.) that have made homes out of a wide range of empty shells!
Although they look soft, some snails can drill holes through the shells of their prey. These snails are conveniently called Drills!

Drills (Family Muricidae) that live on the rocks prey on other shelled creatures, especially barnacles. To bore a hole through the victim's shell, a drill softens the shell with an acid secreted by a special gland on the underside of its foot. A hole is slowly created with a little help from its rough 'tongue' (called the radula). It can take eight hours for a drill to get through a shell 2mm thick. Yawn!
It is common to encounter drills on our rocky shores huddled together to lay masses of bright yellow egg capsules. Each egg capsule may contain 20-40 eggs. The egg capsules turn purple when the free-swimming larvae hatch.

Marine snails are among our favourite seafood. These include the Gong gong and other Conch snails, Chut Chut and other Creeper snails. Abalone is a gastropod and not a bivalve! Wild populations of this snail is under severe pressure from over collection.

Many snails are also killed merely for their shells.
Cowries are among the most sought after shells. Living snails are harvested and killed for the shell trade. The living snail, however, is often more beautiful than its empty shell.

Sadly, many of our beautiful and fascinating snails are listed among the threatened animals of Singapore. Like other marine creatures, they are vulnerable to habitat loss due to reclamation or human activities along the coast that pollute the water. They are also vulnerable to trampling by careless visitors and over-collection for food and for their shells can affect local populations.
This large and beautiful Bailer snail (Melo melo) is among those listed among Singapore's threatened animals and is now only sighted on a few of our shores.