King crab

King crabs live in the deep, cold sea.

They look like true crabs. But they are actually close to hermit crabs. Some live in very deep water. Others live in shallow water. They have five pairs of legs. One pair is for grabbing things. The other legs help them walk. Some people catch them for food. Red and blue crabs are popular. We must be careful not to catch too many. These crabs are very special sea animals.

King crabs live in the cold, deep sea.

They look like true crabs. But they are actually close to hermit crabs. Scientists think they used to be hermit crabs. Long ago, they grew hard shells and left their snail shells behind.

There are two main groups of king crabs. The first group lives in deep water. They can be found in all five oceans. The second group lives in shallow water. These only live in the North Pacific. They can handle warmer water than the deep ones.

King crabs have five pairs of legs. The first pair are chelipeds. These are claws used for grabbing. The next four pairs help them walk. They have a short body part on their underside. In some crabs, this part is soft. In others, it is hard.

Many people catch king crabs for food. Red and blue crabs are very popular in Alaska. People also catch golden king crabs there. In South America, people catch southern king crabs. We must be careful not to catch too many. This helps keep the crab groups healthy.

King crabs are amazing sea creatures. They belong to a group called Lithodidae. These animals live in cold water. They are very different from true crabs. Most scientists think they are close to hermit crabs. This is a process called carcinisation. It is when an animal starts to look like a crab.

They are divided into two main groups. The first group is called Lithodinae. These crabs live in very deep water. The second group is called Hapalogastrinae. These live in shallow waters in the North Pacific.

Let's look at how a king crab is built. They have five pairs of legs. The first pair are called chelipeds. These are the large claws used for grabbing. The next four pairs are walking legs. These legs end in sharp tips called dactyli. The fifth pair is very small. These tiny legs help the crab clean itself. On their underside, they have a short abdomen. This part is called a pleon. In some crabs, the pleon is soft. In the Lithodinae group, the pleon is hard and calcified. This means it is covered in a tough, stony layer.

Learning about these crabs has taken a long time. Zoologist George Samouelle created the family Lithodidae in 1819. He named the first group Lithodes. Later, experts studied how they are related to other animals. In 2007, Patsy McLaughlin and her team moved them to a new group. They called this group Lithodoidea. This was a very controversial idea. Most experts believed they were still related to hermit crabs. In 2023, scientists moved them back to the hermit crab group.

King crabs live in many different places. The Lithodinae group lives in all five oceans. This includes the Pacific, Atlantic, Indian, Southern, and Arctic oceans. Some live very deep. The genus Lithodes lives at 2,500 meters deep. The genus Neolithodes lives at 1,500 meters deep. The genus Paralomis lives at 1,000 meters deep. The Hapalogastrinae group stays in shallow water. They can live in warmer water than the deep crabs. Some crabs even live near hydrothermal vents. These are places on the ocean floor that release heat.

Humans interact with king crabs in many ways. Many people catch them for food. Red and blue king crabs are very popular in Alaska. People also catch golden king crabs there. In South America, people catch southern king crabs. Some of these populations have declined because of overfishing. Other animals live with the crabs too. Some small fish lay eggs in the crab's gill chamber. This keeps the eggs safe and gives them air. Other tiny animals, like certain barnacles, can live on the crabs. These relationships show how busy the ocean floor is.

King crabs, also known as stone crabs, are marine decapod crustaceans from the family Lithodidae. These animals are highly specialized for life in cold environments. While they look like true crabs, they are actually closely related to pagurid hermit crabs. This relationship is a famous example of carcinisation, a process where an animal evolves to look more like a crab.

King crabs are important to ocean ecosystems and human economies. They are found in deep waters and are often targeted by commercial fisheries.

The anatomy of a king crab is quite complex. They possess five pairs of legs known as pereopods. The first pair are the chelipeds, which are large claws used for grasping. In many species, the right cheliped is larger and more robust than the left. The second, third, and fourth pairs are walking legs that end in sharp points called dactyli. The fifth pair is very small and is used for cleaning. These tiny legs usually sit inside the branchial chamber, which is the area where they breathe. On their underside, they have a short abdomen called a pleon. This abdomen consists of six segments, called somites, and a telson. In the subfamily Lithodinae, this abdomen is hard and calcified. In the Hapalogastrinae subfamily, the abdomen remains soft.

Scientists divide the Lithodidae family into two distinct subfamilies. The first is Lithodinae, which contains most of the family's species diversity. These crabs are globally distributed and typically inhabit very deep waters. The second subfamily is Hapalogastrinae, which is endemic to the North Pacific. Unlike their deep-sea relatives, Hapalogastrinae live exclusively in shallow waters. They also show a higher tolerance for warmer temperatures than the Lithodinae.

The history of king crab classification has seen much debate. Zoologist George Samouelle established the family Lithodidae in 1819. He created the family to include the genus Lithodes. In 2007, carcinologist Patsy McLaughlin and her colleagues proposed a change. They moved king crabs into a separate superfamily called Lithodoidea. This was controversial because phylogenetic evidence suggested they were still related to hermit crabs. In 2023, scientists resolved this by folding king crabs back into the Paguroidea superfamily.

King crabs inhabit a vast range of ocean depths and regions. Lithodinae members can be found in all five oceans: the Pacific, Atlantic, Indian, Southern, and Arctic. Some species live at extreme depths. For example, members of the genus Lithodes have been found at 2,500 meters. The genus Neolithodes lives at 1,500 meters, and Paralomis lives at 1,000 meters. They are often found near hydrothermal vents and cold seeps.

Human activity significantly impacts king crab populations through commercial fishing. Red and blue king crabs are heavily targeted in Alaskan waters. The golden king crab is also a major target in Alaska. In South America, fisheries focus on the southern king crab and several Paralomis species. However, some populations have faced serious trouble. The southern king crab has seen a dramatic decline due to overfishing. Some fishing areas must be closed entirely to protect the remaining crabs.

King crabs also host many other living things. Juvenile Neolithodes diomedeae live on sea cucumbers called Scotoplanes. This is a commensal relationship, meaning the sea cucumber is not harmed while the crab gets protection from predators. Some species of careproctus fish use the crab's gill chamber to lay eggs. This provides a safe, aerated environment for the eggs to hatch. However, some relationships are more harmful. The rhizocephalan barnacle Briarosaccus is a parasite that can irreversibly sterilize a crab. In some populations, over 50% of the crabs are affected by these barnacles.