Imagine that you are tanning in the sun, and you feel something nibbling at your toes. You look down and see a ton of little red creatures at your feet. You have no clue what they are. Then, you get a closer look at one of them, and you notice they are… CRABS!!!
You don’t notice one of the crabs has been climbing up your chair. Before you notice it is there, it bites you. Ever since then, you have been very interested in crabs.
What is a crab?
A crab is a small sea creature. Crabs live in shells and they don’t move very fast. All crabs have eight walking legs and two claws. There are about 45,000 types crabs that come in many different kind of colors.
How do they move?
Some crabs live on land and others live in the water. The crabs that live in the water have paddles on their back legs. This is what makes them able to swim. Crabs that live on land have eight walking legs which are on the backside of the crab’s body make the crab walk either right or left. One side of the 8 back legs helps pull the crab, and the other four stretch out and push. The crab usually doesn’t move straight forward.
A crab has three main parts on its body. It is hard to see those parts if you look at the crab from above. You have to flip the crab over to see the parts because the carapace covers it. A carapace is the main part of the body where the shell is hard. Its head and the middle part of the body are called the thorax. The cephalothorax is what joins the head and the middle section together. The legs are mostly used for transportation. The front two legs of the crab are the closest to its head. They are sometimes used for walking but mostly used for eating. Those two legs are called chelipeds. The claw/pincher on the cheliped is called chela. The chelas are used to grasp or hold something. The pinching part located on the front of the crab’s body is the claws. The claws help the crabs catch their prey. Sometime crabs get so scared of humans that when they pinch the person their claw breaks off. Soon after a claw breaks off, a new on will grow on.
Crabs have a soft inner layer and a hard outer layer. Animals with this type of body are also known as crustaceans. Crustaceans are also known as decapods. Decapods are 10-footed animals. Other decapods are lobsters and shrimp.
How female crabs hatch their eggs
When the female crab has baby crabs, they come out in eggs. When the female crab lays her eggs, she puts them in water. Then she moves fast above the eggs, so that they will hatch. When the baby crabs hatch, they are called larvae. They don’t look at all like the adult crabs. They have to go through stages of their life before they look like a crab.
The stages of a growing crab
During the first stage, the crab is known as a zoea. The zoea is very tiny and looks a lot like a shrimp. When the crab is a zoea, it is usually about 1 millimeter (1/ 25 inches) long. The zoea usually feeds only on the larvae of oysters and starfish. The zoea starts to shed the outer layer of its shell because it is getting big. This is called molting.
When the crab enters its second stage of growing it is called megalops. This means that it has large eyes. The megalops also gets its claws and the appendages of an adult crab. This shows that the crab is almost done growing.
During the final stage, the crabs are full grown. The megalops on the crab molts. Then a young crab has all of the body parts that an adult crab has. The hard part that gets made during this process is called a chitin. A chitin is the hard part of the crab also known as a carapace. When the crab grows, the chitin grows with it. The chitin stays with the crab for its whole life.
How do male crabs find their mates?
Some male crabs find their mates by waving their claws up in the air. This helps them find female crabs of their own species. Other crabs will drum their claws on a hard rock, so that they can attract a female crab of their species. Each specie of crab has a different way of finding its mate. When the male crab finally finds its mate, the male will put its sperm into the female’s body. When the sperm gets to the female’s eggs, more crabs will be produced.
What do certain kinds of crabs eat?
Coral crabs, which are found in warmer parts of the tropical oceans, get their food from coral polyps. These are tiny animals which create coral reefs. Ghost crabs and fiddler crabs eat mud and sand off the beach.
Pebble crabs and box crabs use their claws to crack open marine snails. Then the crab pulls out the soft body that is inside it. It holds the soft body up to its mouth where the mouthparts tear it apart and eat it.
How do certain crabs camouflage themselves?
Hairy crabs’ hair helps them when they see an enemy. First, they find seaweed. Then they blend in with it. When blending in, the enemy usually doesn’t notice it is there. Another crab that has good camouflage is a ghost crab. A ghost crab can camouflage by going into shallow water. All that sticks out is their tall eyes. The eyes look like sticks, though, and the enemies do not notice them.
Coral crabs defend themselves by using anemones. These are soft sea creatures which have stinging tentacles. To defend itself, the crab picks up the anemone and waves it in the air so that the attacker can see it. This usually makes the attacker scurry away because it doesn’t want to get stung.
Hermit crabs don’t usually get to be that big. Even though they live in a shell, they do grow. Their exoskeleton, the shell part of the crab, will fall off during a short period of time. That is because the hermit crab is getting too big to live in that shell. Soon after the old shell falls off, a new shell will grow back.
How do people harm crabs?
People harm crabs by because they will catch them and take them put of there habitat. The people will either take them as pets or the will eat them.
When you finally finish researching crabs, you go back to the same spot you saw the crabs. Now you don’t see a crab you see…(Find out in Rachelle’s Report)
Johnson, Sylvia A. Crabs. Tokyo, Japan: Learner Publications Company, 1982.