Crab

Crabs have a hard shell to protect them.

Many crabs can run sideways. This helps them hide in rocky cracks. Some crabs are very tiny. Others are very large.

One big crab lives on land. It is the largest of its kind. Some crabs live in salt water. Others live in fresh water.

People often keep hermit crabs as pets. They are very interesting animals.

Crabs are many different kinds of animals. They are not all in one single group. Most crabs belong to a group called Brachyura. These are known as "true crabs."

Other animals, like hermit crabs, look like crabs too. This happens through carcinisation. This is a way where different animals grow a similar body shape over time.

Most crabs have a hard shell called a carapace. This shell protects their soft bodies. Many crabs can run sideways. This helps them hide in rocky cracks.

Crabs come in many sizes. The pea crab is only a few millimeters wide. The Japanese spider crab has a very large leg span. The coconut crab is the largest animal like this that lives on land.

Crabs eat many different things. Some eat plants like algae. Others eat small animals. Some even eat bits of waste. People also eat crabs. They are a common food in many parts of the world.

Crabs are amazing creatures found in many different parts of the world. They are not all part of one single family tree. Instead, many different groups have grown to look like crabs over a long time. This process is called carcinisation. It happens when different animals develop a similar body shape to survive. Most crabs have a hard shell called a carapace. This shell acts like armor for their soft bodies. Many crabs can also run sideways to move quickly.

How a crab works depends on its specific body plan. Most true crabs have a wide, flat shell and a tucked-under tail. This shape helps them squeeze into tiny rocky cracks to hide. Some crabs, like the porcelain crab, use tiny hairs to filter food from the water. Other crabs, like the yellow moon crab, are hunters that eat other animals. Hermit crabs have a different way of staying safe. They do not have a full shell of their own. Instead, they find empty snail shells to live inside for protection.

Scientists have studied these animals for a very long time. We can see crabs in art from many ancient cultures. The Moche people of Peru showed crabs in their art to honor the sea. In 1495, the artist Albrecht Dürer painted a very detailed crab. Even in stories, crabs are important characters. Rudyard Kipling wrote a story about a giant crab that made the tides move. Some myths, like those from Malaysia, say a giant crab lives in the center of the sea.

Crabs come in many different sizes and types. The tiny pea crab is only a few millimeters wide. On the other hand, the Japanese spider crab has a huge leg span. The coconut crab is the largest animal like this that lives on land. It can weigh up to 4 kilograms. Many people around the world eat crabs as food. About 20% of all marine crustaceans caught are crabs. In the United Kingdom, people enjoy eating the brown crab.

Crabs are part of our daily lives in many ways. You might see them in a seafood meal like crab curry. Some people even keep hermit crabs as pets in aquariums. To keep a hermit crab happy, you need sand and coconut fiber. They also need both fresh water and salt water to live. You might even see the sign for the star sign Cancer. This sign is named after the crab because of its shape.

Crabs are a diverse group of animals known for their armored bodies and unique ways of moving. They are decapod crustaceans, which means they belong to a group of animals with ten legs. While we often think of them as one single family, they actually come from several different evolutionary paths. Most crabs share a specific body shape, including a heavy shell and a tail tucked under their bodies. They are famous for their ability to run sideways, a movement often called "crabwise."

This body plan helps them hide in rocky crevices to stay safe from predators.

Many crabs look similar because of a process called carcinisation. This is a type of convergent evolution where different species develop the same physical traits. In a marine environment, having a wide, flat body and a hard carapace is very helpful. These features allow animals to squeeze into tight spaces and survive being hit by heavy waves. Because several different groups have evolved this way, crabs are considered polyphyletic. This means they do not all share one single common ancestor that looked like a crab.

There are several distinct groups of animals that we call crabs. The Brachyura are the "true crabs," which include about 7,000 different species. Other groups belong to the Anomura, which include hermit crabs, king crabs, and porcelain crabs. King crabs live in cold, deep waters and look like true crabs, but they are actually more closely related to hermit crabs. Porcelain crabs are small and flat, often hiding under rocks. They are unique because they use long, feathery bristles on their mouthparts to filter plankton from the seawater.

Hermit crabs have a very different survival strategy than true crabs. Instead of having a hard shell called a carapace to protect their whole body, they have a soft abdomen. To stay safe, they scavenge empty snail shells to live inside. The coconut crab is a massive version of this, living on land in the Pacific and Indian Oceans. It is the largest terrestrial invertebrate in the world, weighing up to 4 kilograms.

Other crabs, like the tiny pea crab, live as parasites inside other animals like molluscs.

Crabs vary wildly in size and habitat. The pea crab is only a few millimeters wide, while the Japanese spider crab has a massive leg span. While most crabs live in the ocean, about 1,300 species have adapted to freshwater. Some even live entirely on land, like the tree crab, which only returns to the ocean to spawn. The Christmas Island red crab is famous for its annual mass migration to the sea to lay eggs.

Humans have interacted with crabs for thousands of years through food and art. Crabs make up about 20% of all marine crustaceans caught or farmed for humans. This equals roughly 1.5 million tonnes of crab meat every year. In Japan, the snow crab is a winter delicacy served as sushi. In the United Kingdom, the brown crab is a popular seafood choice. Crabs also appear in history through art, such as the paintings of Albrecht Dürer in 1495.

Crabs even hold a place in our stories and the stars. The constellation and astrological sign Cancer is named after the crab. In Greek mythology, a crab named Karkinos helped the Hydra during its battle with Heracles. Rudyard Kipling wrote a famous story called "The Crab that Played with the Sea" about a giant crab. This story is often linked to the horseshoe crab, an ancient creature that has existed for 445 million years.