Today, science knows 93 families of crabs. They include about 7 thousand species. Among them there are small ones, no larger than a spider, and truly huge ones. There are poisonous and crabs with unusual appearance. These include varieties that are kept in home aquariums.
In this article we will look at the most popular crabs, photos and varieties of these marine inhabitants.
general description
These animals are classified as crustaceans and belong to the order Arthropods. Representatives of all varieties of crabs (the names and photos of some are presented in the review) have 10 limbs, thanks to which they are able to move quite quickly. In addition, they have a pair of claws. They are larger than the other limbs and are sometimes asymmetrical. Crab claws serve two functions. The first is eating food. They are powerful and sharp enough to tear off chunks of food. In addition, the claws are weapons that help them protect their lives and compete with their brothers. Often in such battles the animal may lose one limb. However, pretty soon a new one grows in its place. This explains the asymmetry of the claws.
Limbs can have different shapes. It depends on the type of crab. Some have the last pair of legs shaped like oars. Thanks to this feature, they swim faster than their relatives.
The body of these animals also differs depending on the type. Some representatives of certain varieties of crabs have a round shape, others are triangular. It is noteworthy that in nature there are even individuals with a square body. It, in turn, smoothly passes into the cephalothorax. This part of the body got its name due to the fusion of the chest and head parts. The eyes are located on stalk-like processes. The body of this animal is protected by a durable chitinous shell. It serves as a kind of exoskeleton for the crab, which protects the internal organs from possible damage. During periods of molting, the crab's protective cover becomes soft. During this process, new, durable chitinous plates are formed. The animal sheds its old shell.
Natural enemies
Adults are practically not afraid of anyone, because arthropods are protected by a hard chitinous cover in the form of a shell. In addition, special needles in the form of spikes are located on the surface of the carapace. Only large mammals can overcome such protection. Young individuals cannot boast of such protection, so they have many enemies. These are predatory fish:
- halibut;
- cod;
- bulls.
As well as sea otters and octopuses, other large arthropods.
The most vulnerable time is molting. Therefore, during this period, he hides in secluded places so that no one can reach him.
Man is not a natural enemy, but the fact that many people bypass the law and catch these animals without a license may indicate that man will become enemy number one for underwater inhabitants.
Thanks to established state quotas, today the catch of Kamchatka crabs is limited. The state is trying to curb population decline so that arthropods can reproduce and maintain populations.
Russian crabs
The most valuable type of crab for fishing is the blue one. This crustacean is large in size and weighs up to 5 kilograms. This type of crab got its name from the blue spots located on its body. However, the predominant color in its color is brown.
This type of arthropod is found in the Sea of Okhotsk and Bering Sea. Interestingly, the color of these crabs differs depending on their habitat. Specimens from the Sea of Okhotsk have a brighter color than specimens from the Bering Sea.
In addition to the blue crab, other species are also found in Russia. Not all of them are of commercial importance, but they are no less interesting animals.
Lifestyle and habitat
King crabs tend to become sexed when at great depths. Social and colonial characteristics appear in juveniles between 1 and 4 years of age, when they flock or form large groups of individuals. The association occurs at shallow depths and is used for protection. King crabs are natatoric, or adapted to swimming, when they are in the pelagic stage as a free-swimming planktonic larval form.
Representatives of this species usually live in shallow coastal waters less than 60 meters deep with flat topography, such as in Bristol Bay in southwestern Alaska and Kamchatka, although they go to depths of up to 200 meters. Blue crabs also live in waters about 200 feet deep and are often found off Pribilof Island and St. Matthews Island in the Bering Sea. Golden king crabs live deeper, such as around the Aleutian Islands and Adak Island, where they live at depths of up to 500 meters. However, as a rule, they stay in waters at a depth of 200 to 400 meters. Golden king crabs prefer habitats consisting of soft corals and boulders, while blue and red king crabs prefer sandy or muddy ocean bottoms.
Kamchatka crabs
This species has long been under the supervision of both scientists and ordinary lovers of marine animals. And this is not at all accidental. Kamchatka crabs are quite rare and unusual creatures. They are one of the largest arthropods. It is noteworthy that the name “Kamchatka crab” does not mean one specific species, but several. All of them live in the Far East. The main types of Kamchatka crab are:
- equal-spined crab;
- crab blue;
- barbed;
- snow crab Opilio;
- Baird's snow crab;
- quadrangular hairy;
- Red snow crab.
At the restaurant
When ordering crab, you can ask the chef to cut it before serving (serve it open) - this is the simplest solution to the problem.
For self-cutting, the guest will be given tools: scissors-tongs, a long knitting needle with two tiny teeth at the end and an ordinary fish fork. The correct procedure in this case:
- Twisting of claws and paws;
- Crushing them with tongs;
- Cutting the shell with scissors, removing the gills and stomach;
- Removing meat from the paws using a knitting needle, and from the claws using a fork;
- Eating meat from a rosette.
Attention! On one side of the seafood fork there is a small spoon - it is used to scoop out juice, sucking it out is contrary to the rules of etiquette.
The waiter will also bring a damp cloth or a bowl of water - they are needed for washing your hands after the meal.
marble crab
This species has a square, flat shell. Its distinctive features are its agility and tiny size. This animal breathes using gills. It is noteworthy that its claws are different from each other. The right limb has large curved teeth. However, the left claw has tightly interlocking small teeth. The legs of this arthropod are completely covered with hair. The color of the shell can vary from green to purple. At the same time, the pattern on the shell is externally similar to the waves of marble, for which the animal got its name.
This crustacean lives, as a rule, in the coastal zone. Marbled crabs can often be found basking on rocks.
Where do they live?
Over the many millions of years during which this class has existed on the planet, its representatives have perfectly adapted to different living conditions. They can be found in the seas of all oceans, in different climatic zones - from the tropics to the Arctic and Antarctic, in waters of different salinity and temperature.
Most crustaceans live in the seas, but there are species that have adapted to life in fresh waters - Japanese or Chinese mitten crabs. They were accidentally brought with ballast waters to Europe and settled along the western shores. This crab is often found in the rivers of Sweden, Germany, and France.
There are even land species. This is the palm thief. Its larvae live in the sea, and adults move to land, entering the water only to reproduce. They have become so comfortable on the shore that they deftly climb palm tree trunks in search of food.
Blue crab
The width of the shell of representatives of this species of crab can reach 20 centimeters. Moreover, males are larger than females. The weight of adult animals can reach 1-1.2 kilograms. Blue crabs have brown, gray and blue shell colors. At the same time, there are several orange spikes on it. They serve as protection for this arthropod. Each spine can reach a size of 7-8 cm. The lower part of the shell and abdomen of the blue crab is light in color.
The claws of these creatures have different shades. It depends on the sex of the animal. In males they are bluish, and in females they have a reddish tint.
Blue crab is of particular value due to the taste of its meat. It is considered a delicacy. For this reason, this type of crab was subjected to active extermination. Today it is listed in the Red Book.
Reproduction
Preparations for the mating process occur after the winter molt at sea. The female is capable of laying up to several thousand eggs. She spawns eggs on the abdominal limbs, and the male fertilizes them. The incubation process lasts several months. The eggs hatch into tiny larvae that settle on nearby plants until they develop into small crabs. As they grow, they change their shell several times during molting.
Determination of gender
Males and females are distinguished by the shape of their underbelly. In females it is round and large, while in males it is wedge-shaped and elongated, smaller in size. Males are also larger than females in size and limb length.
Shedding
Young representatives quickly grow out of their shell and the molting process occurs. It is regulated by internal enzymes that form a new shell while still inside the old one. During molting, even the walls of the intestines and some internal organs are replaced, and the lining of the eyes is replaced.
The old shell breaks on the sides and on the abdomen, and the crab crawls out of it. This process takes no longer than half an hour. Their new shell is still soft and is not able to protect the animal. Therefore, they hide under stones and driftwood until their shell hardens.
Herbal crab
This species is widespread on the Black Sea coast. The name of this animal is due to its unique camouflage abilities. He can literally dissolve in algae. It eats mainly carrion. He clears the coastal zone of it.
The shell of this crab is colored green. The abdomen is pale orange or white. The size of the shell does not exceed 8 centimeters in length and 6 in width.
Application
Crab meat is a very valuable food product. The live weight of meat occupies about 42% of the total body weight. About one and a half billion tons of crabs are caught and grown in the world every year. Raw meat is gray in color and has a jelly-like consistency. It is not eaten raw. It must first be thermally treated.
The composition contains essential amino acids and glycogen, thanks to which the meat has a pleasant sweetish taste. The meat also contains biologically active phosphorus, sulfur, and magnesium. The limbs and abdomen of the crab are eaten. There is a red film under the shell. When molting begins, this film is transformed into a new shell.
Crab meat brings great benefits to the body for various disorders in the hematopoietic system. It is recommended to use it to improve the quality of vision. This is a good prevention of heart and vascular diseases. The calorie content of meat is low, 100 g of product contains no more than 72 kcal, proteins - 18 g, fats - 0.5 g, and no carbohydrates. This is a low-calorie product that is recommended to be included in the diet menu.
Despite the benefits of seafood, it can be harmful to health. Its diet includes not only live food, but also carrion. Animal remains may contain parasites and infections. Eating contaminated meat is fraught with various complications - deterioration in the quality of vision, poisoning, disturbances in the functioning of the central nervous system. Those who suffer from allergic reactions to seafood are prohibited from eating meat.
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sand crab
These animals are small in size. They love to bury themselves in the sand, which is why they got their name. They have an oval shell that can reach 4 centimeters in width. His legs are short, which, however, does not prevent him from moving quickly. A distinctive feature of this animal is its ability to swim in the water column.
Large claws. They seem disproportionate for a crab of this size. The claw fingers are dark in color. Sometimes they are black.
Reviews
People speak positively about crabs. Owners are attracted by the beauty of the arthropod, so they don't need to take too much care of the crab. At home, it is better to keep them in a separate tank, because clashes and conflicts occur. Another disadvantage was the frequent replacement of water. But still, the owners are not ready to give up crabs and these disadvantages can be easily corrected.
Aquarium varieties of crabs
These unique crustaceans have become favorite pets among aquarium enthusiasts. Today, in almost any pet store you can buy varieties of aquarium crabs that survive well in an artificial environment. When choosing such a pet, it is worth considering its size and the temperature of the water in which it will be kept. For some types of crabs, aeration and warm water at least 20-25 degrees Celsius are very important. Animals brought from the northern regions, on the contrary, require cooler water.
Names of varieties of crabs intended for keeping in aquariums:
- Dutch crab. Ideal for beginners. Easy to care for. The optimal water temperature is 24-25 degrees Celsius. The animal does not need dry land.
- Leopard crab. Got its name for its bright color. Goes well with aquarium fish. Like Dutch crab, it does not require sushi. Neighborhood with frogs is undesirable. The optimal temperature is 22-28 degrees Celsius.
Crustaceans are omnivores. In the wild, they are assigned the role of coastal orderlies. Unfortunately, today some of them are on the verge of extinction. As a rule, the person is to blame for this.
Suitable neighborhood
Crabs are territorial creatures that prefer to be alone. They treat their neighbors poorly and have conflicts even with members of their own family. They also show dissatisfaction with other aquarium inhabitants, trying to catch up and pinch the fish. But, if you want to diversify your aquaterrarium, you can choose suitable pets as neighbors for the crabs. This:
barbs
zebrafish
guppy
mollies
swordtails
macrobrachium shrimp
Diet
Crabs need to be fed both animal and plant foods.
They willingly eat:
- pieces of fruit: melon, banana, peach;
- leafy vegetables;
- zucchini, cucumbers;
- raspberries;
- seaweed;
- leaves of aquatic plants.
The following are used as animal feed:
- pieces of krill and squid;
- sea fish;
- mussels;
- pieces of boiled chicken;
- bloodworm, coretra, tubifex.
You can feed granular or tableted commercial food for crustaceans.
Professionals provide food rich in calcium so that the external skeleton is strong. The best option would be grasshoppers. They contain, in addition to a large amount of protein, chitin, which is necessary for building the shell of crustaceans.
It is recommended to give food at least 1 time per day; it is better to divide the volume into 2-3 portions and give it in parts so as not to pollute the water with uneaten leftovers. If only crabs live in the aquaterrarium, it is better to place pieces of food on land.
Choosing a pet for your home
When choosing a pet, you need to evaluate it:
- Dimensions. The larger the adult, the larger the volume of the aquaterrarium is needed.
- Character. It’s worth weighing the prospect: if the crab lives alone, you can get the most aggressive one. And when there are already inhabitants in the reservoir, you should consider how peacefully they can coexist.
- Popularity. Every aquarist wants to become the owner of an unusual species. But a lack of information about rare representatives of crayfish can lead to the death of the animal.
You must first obtain the most complete information about the crustacean from reliable sources. It is better to purchase a crab at a pet store so as not to buy a sick individual.
