Gastropod

Gastropods are a huge and diverse group of animals without a backbone, known commonly as snails and slugs. They belong to a group called mollusks and are one of the most successful animal groups on Earth, with about 65,000 to 80,000 living species. This makes them the second-largest group of animals after insects.

These creatures live in many different places, from the deep sea to mountains, rivers, gardens, and even 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 amazing 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 ancient Greek words meaning "stomach" and "foot". This name refers to how a gastropod's "foot" is located below its body.

Earlier, these animals were called "univalve" because they usually have one shell. This is different from bivalves, like clams, which have two shells.

Diversity

Gastropods, which include snails and slugs, are incredibly diverse animals. They are second only to insects in the number of different types of species. Scientists estimate there are between 50,000 and 120,000 named species of gastropods, with even more that have not yet been discovered.

Many gastropods live in the ocean, especially on the slopes near continents, while fewer live in deeper parts of the sea. There are also thousands of species that live in freshwater and on land. Scientists believe many more species exist, especially in the deep sea, where very little has been explored.

Habitat

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

Gastropods live in many different places, both in water and on land. You can find them in deep ocean trenches, fresh water, 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 even live in extreme places like hot underwater vents or very deep ocean trenches.

Anatomy

Snails go through a special twist called torsion during their growth. This twist moves their back end up and over, so their opening, called the anus, ends up near their head. This twist helps them pull their heads in more easily 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, either 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, which include snails and slugs, have interesting ways of growing from eggs to adults. They start by laying eggs, and from these eggs, tiny embryos develop. Some young gastropods go through a special stage called larvae before becoming adults.

Some gastropods rest during hot or cold times, known as estivation or hibernation. When it's time 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. Those that live in the ocean can be plant eaters, meat eaters, or even eat dead animals. Land snails and slugs might eat leaves, fruit, mushrooms, or even dead insects.

Some land gastropods like to eat mushrooms and other types of fungi. They can eat many kinds of mushrooms, such as oyster mushrooms and others. These eating habits help break down plants and fungi, which is important for nature.

Genetics

Gastropods show interesting differences in how their genes are organized compared to other animals. Big changes in gene arrangement happened when certain 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, but scientists aren't always sure if they were true gastropods.

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, especially during big shifts like the movement of ice sheets in the Pleistocene epoch.

Taxonomy

Further information: Changes in the taxonomy of gastropods since 2005

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

Current classification

Gastropods are grouped into several main categories based on new scientific studies. These groups help scientists understand how different types of snails and slugs are related. The main groups include:

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

History

Scientists have tried to organize gastropods into groups for a long time. Earlier ways of grouping them have changed as we learned more from studying their DNA. Today, scientists use new methods to better understand how these creatures are related, but the groups are still being updated as we discover more.

Ecology and conservation

Many gastropod species are in danger because of loss of their homes, pollution, and changes in the weather. 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.