Gastropod

Gastropods are a large and diverse group of animals without a backbone. They are commonly called snails and slugs. They belong to a group called mollusks and are one of the most successful animal groups on Earth.

These creatures live in many different places, from the deep sea to mountains, rivers, gardens, and deserts. Some have shells that they can hide in, while others, called slugs, either have no shell or a very small one inside their bodies.

Because there are so many kinds of gastropods, they show many differences in how their bodies work, how they behave, what they eat, and how they have babies. This makes them very interesting to scientists who study how animals change and adapt over time.

Etymology

The word gastropod comes from old Greek words for "stomach" and "foot". The name describes how a gastropod's "foot" is under its body.

These animals were once called "univalve" because they usually have one shell. This is unlike bivalves, such as clams, which have two shells.

Diversity

Gastropods, like snails and slugs, are very diverse animals. They have more species than any other group except insects. Scientists think there are between 50,000 and 120,000 known species of gastropods, and probably even more that we haven't discovered yet.

Many gastropods live in the ocean, especially near the edges of continents. Fewer live in the deep sea. There are also many species that live in rivers and lakes, and on land. Scientists believe there are many more species in the deep sea that we have not found yet.

Habitat

Main articles: sea snail, sea slug, Terrestrial animal § Gastropods, land snail, semi-slug, and slug

Gastropods live in many places, both in water and on land. You can find them in the ocean, lakes, rivers, deserts, and even near the Arctic and Antarctic areas. They have adapted to survive in almost every kind of environment on Earth.

Some gastropods, like land snails and slugs, live on land. Others live in water, with most species found in the sea. In places where it’s hard to build strong shells, you’ll often find slugs or snails with thin, see-through shells. Some special snails can live in extreme places like hot underwater vents or very deep ocean trenches.

Anatomy

Snails go through a twist called torsion as they grow. This twist moves their back end up and over, so their opening ends up near their head. This helps them pull their heads in when they are scared.

Most snails have a shell on their backs. These shells are usually spiral-shaped and made of a strong material. Some snails, called slugs, have a very small shell or no shell at all. The shells can twist to the right or the left, and this affects how the snail’s body works inside.

Snails have heads with tentacles that help them feel their way. Some tentacles have eyes on them, helping snails see, even though they don’t see very well. Snails also have special organs to smell and taste their environment. Their bodies have systems for eating, breathing, moving around, and getting rid of waste, all helped by fluids that flow through them.

Life cycle

Main article: Reproductive system of gastropods

See also: Mating of gastropods

Gastropods, like snails and slugs, have fascinating ways of growing from eggs to adults. They begin by laying eggs, from which tiny embryos develop. Some young gastropods go through a special stage called larvae before they become adults.

Some gastropods rest during very hot or very cold weather, a process known as estivation or hibernation. When the time comes to grow up, they mate, and their babies develop either inside or outside the parent’s body, depending on the type of gastropod.

Feeding behavior

Gastropods, such as snails and slugs, eat many different things depending on where they live and their species. Ocean gastropods can eat plants, meat, or dead animals. Land snails and slugs might eat leaves, fruit, mushrooms, or dead insects.

Some land gastropods like to eat mushrooms and other types of fungi. These eating habits help break down plants and fungi, which is important for nature.

Genetics

Gastropods have interesting differences in how their genes are organized compared to other animals. Big changes in gene arrangement happened when groups like Patellogastropoda and Heterobranchia first appeared. In other groups such as Vetigastropoda and Caenogastropoda, there were fewer changes, mostly involving small moves of certain gene pieces called tRNAs. Within the group Heterobranchia, the gene order stays quite similar, with most changes involving the movement of tRNA genes.

Geological history and evolution

See also: List of marine gastropod genera in the fossil record

The first gastropods lived only in the ocean. The earliest known examples come from the Late Cambrian, like Chippewaella and Strepsodiscus. These early creatures had shells that spiraled in a special way.

True gastropods appeared later, during the Ordovician period, and lived in many kinds of water environments. Over time, especially in the Mesozoic era, gastropods became more common and developed many different shapes and sizes. Some of the oldest land snails appeared in the Carboniferous period in Europe, but they were rare until the Cretaceous period.

Fossils of gastropods are found in rocks from both freshwater and ocean environments. These fossils help scientists understand how life changed over millions of years.

Taxonomy

Further information: Changes in the taxonomy of gastropods since 2005

See also: Taxonomy of the Gastropoda (Ponder & Lindberg, 1997)

Current classification

Gastropods are sorted into several groups based on recent science. These groups help scientists see how different snails and slugs are related. The main groups are:

• Subclass Apogastropoda
• Subclass Caenogastropoda
• Subclass Heterobranchia
• Subclass Neritimorpha
• Subclass Patellogastropoda
• Subclass Vetigastropoda (including Neomphaliones)

History

Scientists have worked for a long time to sort gastropods into groups. The old ways of grouping them have changed as we learned more from studying their DNA. Today, scientists use new ways to understand how these animals are related, but the groups are still being updated as we learn more.

Ecology and conservation

Many gastropod species are in danger because their homes are disappearing, pollution is harming them, and the weather is changing. Some of these animals are in danger of disappearing forever, and some have already gone away because of these problems. People work hard to save them by protecting the places where they live, especially in rivers and on land.

Gastropods are eaten by many different animals, depending on where they are. In the ocean, they are eaten by fish, marine birds, marine mammals, crustaceans, and other sea creatures like cephalopods. On land, they are eaten by insects, arachnids such as spiders and harvestmen, as well as birds and mammals.