Bivalvia

Bivalves

Bivalves, also called bivalves, are fascinating water animals that live in both the sea and rivers. They have soft bodies inside a shell made of calcium carbonate. This shell has two parts called valves that hinge together, like a door.

Bivalves do not have a head or some organs like the radula. Common bivalves include clams, oysters, cockles, mussels, and scallops. Most live on the sea floor or in mud, where they eat tiny bits from the water. Some, like scallops, can swim short distances.

People have eaten bivalves for thousands of years. Oysters were farmed by the Romans. Today, farming bivalves, called mariculture, is an important industry. Bivalves also give us pearls, and their shells are used to make jewelry, buttons, and crafts. They help keep water clean, too.

Bivalves have lived on Earth since the early Cambrian period, over 500 million years ago. There are about 9,200 known living species.

The word Bivalvia was first used by Linnaeus in 1758. It describes animals with shells made of two parts, called valves. The name comes from Latin words meaning "two" and "door leaves".

Bivalves have soft bodies inside two shell pieces called valves that are joined together. They do not have a head or some body parts that other sea creatures have. Their bodies are flat and match on both sides.

Bivalves breathe through their gills, which also help them eat by filtering tiny food from the water. Most eat by filtering, but a few eat larger food. Their body processes this food, and they get rid of waste through special tubes.

Most bivalves release eggs and sperm into the water to reproduce, and their young grow into adults over time. Some freshwater bivalves have young that attach to fish before becoming adults.

Bivalves are found all around the world in water. Most live buried in sand or mud on the ocean floor or in freshwater places. Many are found where the ocean meets the land, called the intertidal zone, and in deeper water areas.

These animals live in warm tropical waters and colder areas too. Some bivalves live in very tough places. For example, one type lives under thick ice in the Arctic, and others live near hot underwater vents in the deep ocean.

!Empty shell of the giant clam (Tridacna gigas) Empty shell of the giant clam (Tridacna gigas)

Most bivalves stay in one place their whole lives, often buried in sand or mud under the sea. This helps protect them from waves and some animals that might eat them. They stretch out special tubes called siphons to get food and air when the tide is high and pull them back in or close their shells when the tide goes out.

Some bivalves, like mussels, stick to rocks or other hard surfaces using strong threads. Oysters can form thick layers on rocks and are good at filtering water for food. Even though they filter lots of water, bivalves often close their shells to rest, following patterns set by the moon and sun.

Bivalves like oysters, scallops, clams, ark clams, mussels, and cockles have been eaten by people for a very long time. People cook them or eat them raw. The amount of bivalves traded around the world has grown a lot over the years.

!Flat oysters (Ostrea edulis) from France Flat oysters (Ostrea edulis) from France

Marine bivalves help keep coastal waters clean by eating tiny plants and particles. They take nutrients from the water and put them back on land or change them so they float away. This helps when too many nutrients get into the water from farms and sewage.

Bivalves can collect harmful substances from the water, like heavy metals, because they cannot break these down. This can be dangerous for people who eat them, but it also helps scientists learn about pollution in the water. Crushed shells from bivalves can help clean water by taking away some heavy metals.

Shells are used in many creative ways. They can be pressed into concrete for paths or walls, or used to decorate items like picture frames. Shells can also be made into jewelry, such as necklaces, or used as tools. Some shells have been used for thousands of years by different cultures.

Buttons have been made from shells for a very long time. Shells can also be used to make a special fabric called sea silk. Crushed shells are sometimes added to animal food.

Mother-of-pearl, a shiny layer found inside some shells, is used to make beautiful decorations and jewelry. Pearls are formed when something small gets inside a shell and layers of this shiny material build up around it. Most pearls come from special farms.

The scallop shell is a symbol for many things. It is linked to journeys and travel, and also to ideas about growth and new beginnings. It appears in art, architecture, and even as a company logo.