The coconut crab is considered the world's largest representative of arthropods and, being in reality a hermit crab, and not a crab, belongs to the species of decapods. Its impressive appearance with its huge size intimidates anyone, even the most courageous person. It is better for the faint of heart not to meet such a creature of nature, whose powerful claws can easily break small bones, and even more so not to get acquainted, because there is a risk of an unsuccessful handshake.
Coconut crab: where is found
The habitat of such an amazing monster can be considered the islands of the Indian Ocean, in particular, Christmas Island, where these arthropods are represented in their largest concentration.
Christmas Island is considered a territory of Australia and is located 2,600 km northwest of the city of Perth. Home to the coconut crab, Christmas Island is famous for another feature that has become a tourist attraction and calling card. This is the migration of red crabs, which every year, in the amount of more than 50 million individuals, move from forests to the ocean coast for the purpose of reproduction. Moreover, such a massive trip covers the entire area of the island and takes about a week by time standards. During this period, most of the roads are closed to all modes of transport.
The largest of the arthropods, the coconut crab, has also successfully settled down and feels great in the western part of the islands. Pacific Ocean- the largest ocean on the planet, amazing with a variety of life forms.
Coconut crab sizes
The average growth of such an interesting specimen - a coconut crab is 40 centimeters with a small weight (only about 4 kg); the length of one claw in expanded form can exceed 90 centimeters. The life expectancy of an arthropod is about 60 years, although, according to scientists, this is a controversial issue and this age is due to slowness life cycle may exceed the estimated figure. Coconut crab, whose size at the age of 5 reaches only 10 centimeters, is very popular among exotic lovers; many collectors of curiosities dream of replenishing their collections with such a cute pet.
Coconut crab: description
The body of a coconut crab consists of two halves. The first is a cephalothorax with ten legs, which is the front part, the second half is the stomach. The front, most massive pair of legs is equipped with large claws, while the left claw is an order of magnitude larger than the right one. The next two pairs of legs, like those of other crabs, are powerful and large, ending in sharp ends. Thanks to them, crabs can easily overcome inclined or vertical surfaces. The fourth pair of legs is much smaller than the previous three and allows young coconut crab to nest in coconut shells or mollusk shells for protection. Adults use the fourth pair for walking and climbing. The last pair of legs, the smallest and least developed (as well as the fourth pair), is usually hidden inside the carapace. It is used by males for mating and by females for egg care.
Coconut crab, the photo of which fully conveys it unusual beauty and evokes emotions of uncontrollable fear, in fact, the creature is harmless, unless, of course, you climb on the rampage and try to get to know him better. Otherwise, you can be left without fingers.
Where does the crustacean monster live?
The habitat of the coconut crab is exclusively dry land; in water, an adult cannot live due to the fact that the gill lungs (something in between gills and lungs) are adapted for breathing ground air, despite the fact that the tissues present in the gills are present in such a respiratory organ. Rather, the ability to exist in two environments (aquatic and terrestrial) is present at the initial life stage of the crab, as it matures, such an individual switches to a land lifestyle. In addition, these arthropods do not know how to swim at all and, if they are in the water for more than an hour, they will surely drown. The exception is when the coconut crab is still in its larval stage; in this case water environment is native to him.
Coconut Crab Lifestyle
It is not easy to meet a coconut crab during the daytime, because it prefers to lead a night life, hiding in sunny hours in sandy burrows, coral reef cavities or rock crevices, the bottom of which is lined with foliage and fibers from coconuts. Does it coconut thief- "Crab with a capital letter" in order to maintain an optimal level of humidity in your home.
Also, during the rest, he closes the entrance to his dwelling with one claw. This also contributes to the preservation of a comfortable microclimate for the palm dweller.
First impression of coconut crab
From the point of view of the first Europeans who arrived on the islands where the coconut crab lived, the latter appeared to them as a creature with long claws, hiding in the green foliage of palm trees and suddenly capturing prey passing by or under a tree, among which even goats and sheep came across. Indeed, the palm coconut crab is the most major representative ten-legged crayfish, it has tremendous strength and is able to lift a load weighing about 30 kg. To a greater extent, the crab uses this skill to drag prey from place to place, and in the diet it prefers dead animals, crabs (of course, a little smaller than itself), young turtles and fallen fruits, in particular, pandan fruits and the contents of split coconut nuts. palms. Also, palm thieves (the second name of the coconut crab) were caught catching and eating Polynesian rats and gutting garbage cans, where they are looking for some kind of “yummy”. Moreover, the presence of people is not at all the formidable factor that the palm coconut crab would be afraid of.
The photo clearly conveys the desire of the claw-legged to profit, especially since he has a formidable weapon - huge claws of awesome size.
What does the palm thief eat
Based on the name of this crab, we can conclude that coconuts are its favorite food product. This arthropod can quickly climb palm trunks, and conquering a 6-meter height is quite a familiar activity for it. Looking from the side as a huge multi-legged monster crawls along a smooth tree trunk, along with the delight of such an unusual sight, any person will experience fear and horror from the unusualness of what is happening: it would seem, a crab, an inhabitant of the water element - and on a tree! Isn't it a paradox?! With powerful claws, the crab pinches off coconuts, which fall to the ground and break. If the nut remained intact during the fall, then the coconut crab will aggressively gut it in order to get to the juicy nut pulp; this monotonous process can last more than two weeks. If all attempts fail, the crustacean will achieve its goal in a different way. The palm thief (coconut crab, that is) will lift the fruit back onto the palm tree and drop it down again. Although some reports of persistent cracking of coconuts are unverified; in fact, crabs feed on already split fruits that have fallen from a tree and lie on the ground.
When descending to the ground, crabs, due to their own clumsiness, sometimes do not hold on and fall down. Without prejudice to themselves, they can easily endure a fall from a 4-5-meter height.
Interesting Features of Coconut Crab
Thanks to special organs located on the antennas that determine the direction of the smell and its concentration, the coconut crab, unlike its crustacean relatives, has an excellent sense of smell. Like any crab, it has tactile receptors: hairs and bristles of different lengths. In addition, it has organs of smell, which the rest of its brethren are deprived of. Their presence is due to the specific features of the development of the palm thief, who at one moment could not exist in the water and moved to live on land. Being hungry, he hears his prey even at a distance of several kilometers.
"Palm thief" - the coconut crab got its second name for its love of everything shiny. If any shiny object (be it a spoon, a fork, a metal appliance, household utensils, or something more attractive) meets on the way of an arthropod, the crab will not crawl past and will definitely profit from an interesting find (even if the latter is completely inedible), which it will drag into its crab lair.
Measures taken to conserve coconut crab
Separately, I want to talk about why coconut crab is so valued. A photo of such a monster with huge claws clearly does not cause sympathy for him.
Why do women and men love him so much if there is a constant hunt for such a unique islander? Coconut crab meat, in addition to being considered a delicacy, is also an aphrodisiac (a substance that triggers the process of sexual arousal in the body and increases sexual desire in females and males), which leads to a fairly intense hunt for this species arthropods. It tastes like lobster or lobster meat and is prepared in the same way.
by the most traditional dish on the islands, it is considered coconut crab, served with coconut milk sauce or boiled in such milk for a little more than a quarter of an hour. By the way, in Guinea, in order to save the coconut crab population, it is forbidden to include the latter in the restaurant menu.
In some countries, in order to prevent complete extinction, severe restrictions on the capture of coconut crabs have been established. So, on the island of Saipan, a ban was imposed on catching crabs during the breeding season and on individuals whose shell sizes are less than 3.5 centimeters.
Coconut crab fishing tricks
Although, for the sake of curiosity, it is still interesting how they catch such huge, fearsome centipedes? In the Mariana Islands, they are baited with coconut traps, into which the coconut itself is finely rubbed. Such a bait is left for a couple of days to “sour”, which is necessary for the crab to smell the dinner prepared for it. The trap does not even need to be hidden, it only needs to be tied to some tree so that the crab cannot drag its prey in an unknown direction.
Reproduction of the palm thief
From the beginning of June to the end of August, palm thieves begin to breed. The courtship process continues for a long time, while mating occurs many times faster. For several months, the female bears fertilized eggs on the underside of the abdomen, and at the time of hatching, the female coconut crab releases larvae into sea water during the tide. Over the next three to four weeks, the larvae floating in the water go through several stages of development. After 25-30 days, already full-fledged crabs sink to the bottom, where they settle in the shells of gastropods or in the shells of nuts, gradually preparing for migration to land, which they periodically visit.
How does the development of small crabs
During this period of life, with a shell on their back, crabs are very reminiscent of hermit crabs and wear a house until the moment when the abdomen begins to gradually harden. Further in the development of a young crab, a molting period occurs, during which the arthropod repeatedly sheds its shell.
The final stage of the “growing up” of a young crab is the tucking of its tail under the abdomen, which causes a kind of protective measure against possible damage. As they grow, crabs gradually lose the ability to breathe underwater and soon finally move to their main habitat - on land.
Coconut crabs reach maturity about 5 years after hatching; The maximum size is reached by about 40 years.
Crabs, along with crayfish, are the most famous representatives of the crustacean order (and besides, delicacies that have not subsided in consumer demand for many years). But not all specimens of these animals go for food - sometimes fishermen catch giant individuals worthy of putting them in an aquarium and admiring this miracle of nature. Let's figure out what is the largest crab in the world?
This arthropod, belonging to the order Majidae, lives at a depth of four hundred meters in the Sea of Japan and has a size that boggles the imagination. The largest crab in the world reaches a weight of twenty kilograms, the circumference of its shell is up to one and a half meters, and the length of each limb is almost four meters. The pincers themselves, which are powerful weapon, can be 40 centimeters long in males, females are usually smaller. Crabs of this species strongly resemble huge spiders, which is why they were called "giant spider crabs".
For the first time, a spider crab was described by a naturalist and traveler from Germany, E. Kampfer. The head and chest of an arthropod are protected by a flat shell ending in acute angle. The shell is richly covered with tubercles and spikes, which provides the animal with reliable protection from predators. In addition, the shell contains a huge amount of a substance called chitin, due to which it can resist the pressure of water. The joints in the legs of a crab have very smooth cartilages that reduce friction and allow the arthropod to move only sideways.
Scientists claim that the spider crab can live up to a hundred years, although the exact age of the oldest specimens has not been determined.
The functions of the Japanese spider crab for the ecosystem are approximately the same as those of the vulture bird: it eats the skeletons of dead marine animals, plants and mollusks. Because of this, the meat of adult crabs becomes somewhat bitter. Therefore, only young animals are suitable for human nutrition, and old individuals caught in the net are either released or sent to zoos and aquariums.
In 2013, the largest known representative of the species was caught in the waters near Tokyo - the crab, which was named Kong. The span of his legs was three meters, but the crab is still young and will continue to grow, so that according to forecasts in the future, he will be able to safely ride even a car. At first, the village fishermen planned to make soup from this large animal, but then changed their minds and called a biologist they knew, who came and bought Kong for the British zoo in Weysmouth. Thus, this crab became the largest ever kept in captivity. Soon it is planned to transport it to the Munich Zoo.
The number of these amazing animals is decreasing every year. The fact is that these crabs reach sexual maturity only in the tenth year of life, and until that time they live in smaller areas of water bodies, where there is a high risk of getting caught by poachers or predators. That is why the species is very vulnerable and needs protection. But on this moment the capture of its representatives is not limited to anything. The crab is caught as for eating because of its unusually tasty and tender meat and for decorative purposes.
A specimen of this animal was caught off the Australian coast and weighed seven kilograms, which is much higher than the weight of its other relatives. The shell diameter was 38 centimeters. Its claws are comparable in size to the palm of an adult male. Although this crab is inferior in size to the champion - spider crab - it also looks very impressive.
When it reaches its maximum size, it is predicted to weigh up to 13 kilograms.
The animal, caught by Australian fishermen, was not sent to a restaurant to be eaten, but on the contrary, its quality of life was improved - it was placed in the aquarium of the English city of Weymouth, whose authorities did not regret paying as much as five thousand dollars for a valuable specimen. The crab was brought to the site by plane, so he spent almost 30 hours in flight. We can say that the animal was very lucky, because in its homeland it would be considered a delicacy.
Now Claude (as the arthropod was called) lives in comfort and satiety and pleases the eyes of those who come to look at the curiosity. He is meticulously cared for best conditions for growth and development. By the way, the life span of this species is approximately twenty years, and Claude is still quite young.
It has a second name - Kamchatka and is the largest crustacean in the Far East. Because of the most tender, nutritious and healthy meat, the animal is constantly hunted, including illegal ones. The king crab is a rather impressive and powerful representative of crustaceans, its shell can be up to 26-29 cm wide, its legs span up to one and a half meters, and its weight is up to 7 kg. Strong claws are located on the front pair of legs (moreover, the left claw is usually slightly smaller and weaker than the right one). With his right he gets food: destroys the shells of mussels, sea urchins etc. And the left one is necessary for grinding food and placing it in the mouth.
The king crab has a rather large habitat: the Sea of Okhotsk, the Sea of Japan, the Bering Sea. According to the observations of zoologists, the largest population of crabs lives near the western coast of the Kamchatka Peninsula, and it is there that crab fishing takes place every year.
In the waters of our country, the king crab did not appear by chance, but was purposefully brought into the Barents Sea
Throughout their lives, they constantly travel, moving along a certain route depending on the season and on changes in water temperature. They hibernate at a depth of 250 meters, and in spring they approach the shore to search for a pair and breed. When a whole colony of long-legged crabs moves towards the shore along the bottom, the spectacle is amazing.
During the mating period, the female crab is able to lay an incredible number of eggs, up to three hundred thousand. She carries the formed larvae on her legs for a year. Approaching shallow water, the young hatch from eggs and let them swim independently, and mothers continue to move along their route as if nothing had happened. Unfortunately, most of the small crabs do not have time to grow up, becoming the prey of various marine predators.
Male king crab reach sexual maturity at about 9 years old, females a little earlier.
Here, even the name of the species speaks for itself. However, this crab is better known to the average Russian as brown crab. The body of the crab is oval in shape, with claws of medium length. The shell is usually reddish-brown.
An adult of this crab grows up to 25 centimeters long and weighs up to 3.5 kilograms. Nevertheless, there are cases in science when an animal has reached much larger parameters.
The habitat of a large land animal is the northern part of the Atlantic, but some individuals are even found in the Mediterranean Sea
Crabs are very unusual animals that are constantly hunted because of their meat. Let's hope that the contemplation of the largest representatives of the species will make hunters for easy money think.
Crabs are a large group of aquatic and semi-aquatic animals belonging to the order Decapod Crustacea. Crabs differ from their related crayfish, shrimp, lobsters and spiny lobsters in their noticeably shortened abdomen, tucked under a wide cephalothorax. This gives them a specific, well-recognized form. At the same time, crabs have reached an unprecedented diversity: 6793 species of these animals are united in 93 families, which is half the number of the entire detachment.
Spotted rock crab (Grapsus grapsus) is an inhabitant of the Galapagos Islands.
Along with a special body shape, crabs are characterized by the presence of 10 pairs of limbs. They are divided into chest and abdominal. The first 3 pairs of thoracic limbs are very short, they are called mandibles, because they do not participate in movement, but serve only to bring food to the mouth. The remaining pairs of pectoral legs serve to move, capture and cut food, and can also perform other auxiliary functions. The pair of largest and most massive legs are pincers. With their help, crabs can not only hunt, but also defend themselves, participate in mating battles. The narrow specialization of these bodies was reflected in their appearance: often the right and left claws have a different size and shape, giving the crab's body a noticeable asymmetry. As for the ventral legs, they are small and are used for fertilization (in males) or gestation (in females). Such vital organs as gills are connected with the pectoral legs of crabs. Often their petals are located directly on the segments of the legs or near the place of their attachment to the body.
Because of the huge difference in claw size, fiddler crabs appear to be one-armed. Like people, these animals are right-handed and left-handed, with right-handers making up 85%.
Crabs are one of the most perfect crustaceans, so they have developed sensory organs. Vision plays an important role in their lives. The eyes of these animals are complex, faceted. They consist of thousands of eyes, each of which sees only a tiny part of the space directly in front of it. The final assembly of the image takes place already in the brain of the animal. Numerous observations have shown that with the help of vision, crabs identify a potential enemy, find a partner during the breeding season, and navigate in search of food. But if the animal is blinded, it will only lose the ability to see danger, and find food and a partner with almost the same efficiency. In this he will be helped by antennas ("antennae") that can capture odors. If the crab also cut off the antennae, then it ... will find food again. True, in this case, he will have to spend a lot of time and effort, because he will literally move towards the prey by touch, tapping his claws on the ground. Some types of crabs have balance organs - statoliths. By the way, the eye stalks play a huge role in their physiology. These are real endocrine glands, capable of secreting hormones and regulating body functions such as the frequency of molts, the onset of puberty, and even color change!
The terrestrial bigeye Latreille (Macrophthalmus latreillei) has especially long eye stalks, which is associated with the need to inspect the area at a great distance.
Crabs do not have skin as such; it is replaced by a layer of hard and impenetrable chitin, which forms a kind of shell. Chitin is not able to stretch, which makes normal linear growth impossible. Crabs solve this problem with regular moults. When the old shell bursts, a soft and defenseless animal is selected from it. It takes from several weeks to six months to harden the new cover, during this period the crab hides in a secluded place and grows intensively. Chitin can be impregnated with all sorts of pigments, so the color of crabs can be almost any.
The Bicolor Vampire Crab (Geosesarma bicolor) gets its name from its unusual combination of bright yellow eyes with a deep purple shell. Due to its imposing appearance, it is often kept by amateur aquarists.
In addition, the chitinous cover may have outgrowths: rare and hard, like thorns, short and hard, like bristles, or long and thin, like wool.
Chinese mitten crab (Eriocheir sinensis) stands out among relatives with a "fur" muff on claws.
The sizes of these animals also vary widely. The diameter of the shell of the smallest pea crab in the world does not exceed 1 cm, while the leg span of the largest Japanese spider crab reaches 4 m and weighs 20 kg.
Pea crab (Pinnotheres boninensis) lives on the coast of the Azov and Black Seas.
Crabs inhabit all the seas and oceans of the planet, but they reach the greatest diversity in the tropics. The habitat of these crustaceans has a very wide range: crabs can be found in the shallow waters of the seas and oceans, among coral thickets on reefs, at depths of up to 5000 m, in cave reservoirs, in the tidal zone, mangroves and even in the depths of islands away from the coast. The vast majority of them live in salt water, about 850 species live in fresh water. Crabs that spend a long time on land store water under their shells or develop lungs-like organs. Their underdeveloped gills almost do not work, and with constant immersion in water, such individuals die. Bottom-dwelling species are often active in the dark; land crabs are most active during the day.
The Tasmanian giant crab (Pseudocarcinus gigas), the second largest on the planet, weighs up to 13 kg with a shell width of 46 cm.
When moving, these crustaceans never put both legs of one pair on the ground at the same time, which gives their gait stability, but the short body length and a large number of legs make it uncomfortable to move forward, so crabs prefer to walk sideways. At the same time, this does not in the least prevent them from developing a decent speed, for example, a grass crab overcomes 1 m in 1 s! But these animals swim poorly and reluctantly.
The exception is swimming crabs, in which the back pair of legs is transformed into paddles, thanks to which they feel at home in the water element.
The nature of these crustaceans is quarrelsome, they all live alone and jealously guard their sites or shelters; males are especially aggressive. At the same time, the areas of small crabs are very small, so there can be up to 50 of their minks per 1 sq.m. Danger is the only thing that makes the inhabitants of the colony forget about strife. In the event of a threat, crabs signal their neighbors by waving their claws, making sounds, or tapping on the ground. Thanks to vibrations, even those individuals who do not see the enemy have time to hide.
Blue soldier crabs (Dotilla myctiroides) form large concentrations on the beaches.
Shelters deserve special attention. In the simplest case, these animals hide among coral twigs, in crevices between stones or shell valves, and in sponge cavities. But many crabs do not expect favors from nature, but dig holes themselves in viscous silt or sand. These houses may have one straight passage (often quite deep), or several branched passages with emergency exits; alluring crabs equip the entrance to the hole with a lid. Some species settle under the dome of jellyfish, among the tentacles of sea anemones, in the mantle cavity of mollusks, among needles, or even in the rectum of sea urchins.
These minks on one of the beaches of Malaysia were dug by the closest relatives of soldier crabs - scopimers. Each individual, pushing sand out of the dwelling, rolls it into a neat ball. The droppings of crabs have the same shape when they eat soil.
Crabs have practically no food specialization, they are all omnivores to one degree or another. These animals can eat the bacterial film covering rocks, algae, fallen leaves and flowers, bivalves, polychaete worms, starfish, small crustaceans, and even octopuses. Like crayfish, crabs willingly feast on carrion. Species living in shallow water are happy to “bite” the usual food with soil. Passing sludge through their intestines, they assimilate the microorganisms contained in it. Crabs do not just grab large prey, but butcher it like real gourmets. At the same time, they use claws like a knife and fork: they hold the prey with one, and cut off neat pieces with the other.
A grass crab (Carcinus maenas) is about to dine on a bivalve mollusc.
Reproduction in crabs has a pronounced seasonal character, in different species it is timed to one or another natural phenomena(rainy season, highest tides). For example, Christmas Island red crabs (Gecarcoidea natalis) live on land far from the coast, but move to the surf line to lay their eggs. Their migration is one of the most grandiose phenomena in nature.
Millions of individuals rush towards the goal like a living river, overcoming roads, ditches and other obstacles along the way.
At this time, crabs die en masse under the wheels of transport and the feet of people who are tired of bypassing countless travelers.
To prevent the death of crabs, barriers are being set up along roads on Christmas Island, directing migrants to bypass dangerous routes.
Notice the insects in the frame. These are yellow crazy ants brought to the island by people. They turned out to be a very aggressive and prolific species and have already destroyed 1/3 of the crab population - 20 million individuals!
No less interesting are the mating battles of alluring crabs. With their hypertrophied signal claw, they threaten rivals and even fencing with it in a collision. Then, with waving movements, they give a signal to the female, as if announcing their victory. Such emphasized ritualism has led to the fact that in many species there is a very noticeable difference between males and females (sexual dimorphism).
Duel of alluring crabs.
Before mating, the couple sometimes becomes in a "face to face" position and may remain in this position for several days. Interestingly, one mating is enough for a female to lay fertilized eggs all her life. This is explained by the fact that the male presents her with sperm packed in special bags - spermatophores. In them, germ cells remain viable for many years; during the next season, the female dissolves the spermatophore membrane with special secretions and fertilization occurs again. The fecundity of crabs is very high and amounts to tens of thousands and millions of eggs. The female bears them on ventral legs from a couple of weeks to several months. The hatched larvae are free-swimming.
Swimming crab larva.
After several molts, they turn into young crabs, which settle in biotopes characteristic of a particular species. The life expectancy of these crustaceans ranges from 3-7 years in small species to 50-70 years in a huge spider crab.
Japanese spider crab (Macrocheira kaempferi).
Due to the great diversity and abundance, crabs have many enemies. Fish, octopuses, crocodiles encroach on their lives, sea stars, seagulls and almost all predatory animals wandering on the coast. Raccoons-crayfish generally specialize in picking up crabs on the shore. Such intense interest from carnivores forced these crustaceans to create a variety of ways to protect themselves. The simplest of them is disguise. It is achieved in some cases by coloring, which very accurately reproduces the color and even the pattern of the substrate on which the given species occurs.
The caramel crab (Hoplophrys oatesii) mimics the color and shape of the dendroneftia coral on which it lives.
In other cases, surrounding objects are used for cover. For example, bashful crabs cover themselves with a shield-shell, decorator crabs cut pieces of bryozoans, hydroids with claws and plant them on their backs, gluing them with special secretions. On the back of the crab, these colonial animals continue to develop and turn its shell into a flower bed.
It is difficult to recognize a well-camouflaged decorator crab (Camposcia retusa) in this creeping bush.
Dromia crab looks for a sponge and, like a real seamstress, cuts a piece out of it exactly the size of its back.
Dromia crab (Dromia erythropus) resembles an old woman in a beret. Since his body is rather fleshy, the drome has to look for a flap with a curve that perfectly repeats the bulges of his carapace.
If the disguise did not help, active methods of protection are used. Large crabs become in a fighting stance and raise their claws up. If the hint is not understood by the offender, they use their wire cutters and are able to inflict deep cuts. Boxer crabs always keep anemones in their claws, the stinging cells of which are dangerous even for relatively large animals.
A female boxer crab (Lybia tessellata) in a fighting stance with sea anemones. Egg laying is visible on the abdomen of this individual.
Many species are capable of autotomy (self-amputation). At the sight of an enemy, the crab throws off its leg by contraction of special muscles. At the same time, the valves at the place of separation immediately close the wound and stop the bleeding. If such a handout was not enough, the victim offers the next limb to the predator. Severed legs grow back after several molts.
- Class: Crustacea = Crustaceans, crayfish
- Subclass: Malacostraca = Higher crayfish
- Order Decapoda = Decapod crustaceans (crayfish, crabs...)
- Suborder: Pleocyemata Burkenroad, 1963 = Crabs
- Infraorder: Brachyura Latreille, 1802 = Crabs, short-tailed crayfish
Land (land) crabs
Crabs are Marine life, and it is difficult to imagine that they can live on land, and even more so in trees or in arid regions. Therefore, land-based land crabs are an unusual zoological phenomenon.
The conquest of land by crabs was gradual. Crabs had 10 times less time to conquer land than insects, but their success in adapting to terrestrial existence is very significant. The initial stage of this process is the development of ghost crabs and soldier crabs on tropical beaches. These crabs live in burrows in coastal areas regularly flooded by ocean tides.
Mangrove crabs living on the roots and branches of mangrove trees in tropical rainforests have taken the next step towards land development. All these crabs migrate to the sea for breeding, and after breeding is completed, they again leave for many kilometers from the coast.
Another way for crabs to explore the continents is their adaptation to life in fresh water (see). Along the rivers and streams, these crabs penetrated far into the depths of the continents, climbed the mountains, mastering even the Himalayas. Some crabs, such as the bromeliad crab Metopaulias depressus, have adapted to live in the axils of large leaves of land plants, where rainwater accumulates.
Tropical earth crabs spend their whole lives on land, living in bare desert areas where huge cacti proudly rise above the sands. These crabs can be found at a distance of several kilometers from the sea, where in search of food they roam the clearings overgrown with thorny bushes and barren savannahs. These crabs feed on leaves and other greens.
In the deserts of Australia, thousands of kilometers from the sea, a crab lives, which uses night dew and carries juveniles in a tightly closed “pocket” on its abdomen. The main problem for land crabs is the fight against desiccation. They solve this problem in several ways. Firstly, dense calcareous covers of the body prevent drying out, and secondly, crabs go hunting only at night or after heavy tropical rains, hiding in underground burrows during dry times. In addition, real gills in earth crabs are transformed into a "lung", the respiratory surface of which is moistened due to the presence of tufts of bristles that suck water from the sand. Crab burrows, dug in soft ground, form complex labyrinths several meters long. Often one of the exits leads to a reservoir, due to which high humidity is maintained in the crab's cave.
An extremely unusual respiratory organ was formed in land crabs skopimera and dotilla. These crabs live at the very edge of the water, gathering food on the bare seabed at low tide, and hiding in deep burrows where air is stored at high tide. They breathe with their feet. The hips of the walking legs of these crabs are greatly expanded, and in their middle there is a “window” covered with a thin membrane. In scopimera, windows, the width of the entire segment, are located even on the front claws. In dotilla, they are smaller, but they are also located on the sides of the shell. Previously, it was assumed that these windows serve as organs of hearing, but it turned out that these are real respiratory organs. Crabs with windows smeared with paint begin to suffocate and try with all their might to peel off the paint. Directly under the membrane, inside the segment, there is a complex system of tubules filled with blood. The venous blood passing through them comes into contact with the "gas window" and is enriched with oxygen. The total gas exchange surface of these crabs is large - up to square millimeters, that is, more than that of terrestrial crabs that breathe with their lungs.
Ghost crabs are nocturnal. During the day, they escape from overheating and drying out in deep burrows (up to 1.8 meters deep in large individuals) with a closing entrance. They feed on living crustaceans, mollusks, plant foods (even seeds), and decaying remains. On land, ghost crabs move in sharp dashes at speeds up to 1.8 meters per second on sand and up to 2.3 meters per second on solid ground. Crabs do not avoid humans and even concentrate in places where they find the remains of his food (near baths, beach cafes, etc.).
