Land crab
Biology Category: Animals crab
Animal kingdom, Arthropoda, Crustacea, Decapoda, suborder crawling, crab families.
As the name suggests means living in the land crab, but this one is simple but difficult to apply the definition of the real situation in nature. Because the crabs live on land; still more or less with the sea or fresh water could not escape the relationship, and live crabs in the ocean to the land; also still maintain a certain number of vitality, more life in the intertidal crab , habitat for nearly half the time flooded by seawater, additional time is exposed to air. These crabs how to classify it? Perhaps this is the wonders of nature, things do not always go according to the arrangements simple idea of human classification.
Land crabs nowadays, although most of the land can not be achieved in the full advantage, but the island has been entrenched in many marine food chain, the most senior position, rather there is a rising star in the Earth frame. Land crabs with a powerful fertility, and the spread of larvae drift way to expand its sphere of influence is beneficial to the huge volume to occupy an important niche.
From an ecological point of view, the edge of living species in an ecosystem is often the most resilient species, and land crabs is a product of this environment. Land crabs live mainly on land and sea ecosystems of the intersection of the two areas, they are as long as the face of a small number of competitors, predators are less stringent removal of the natural environment is more competitive species and the number of species, increasing the survival of the species. As the outdoor temperature and land crabs are animals, though not suitable for living in cold regions, but because of low demand for food, it can often reproduce a large number of high-density populations, a more favorable competitive advantage of its existence.
Evolution of the crab from the ocean to life on land, there must be changes in morphology and physiology to adapt to these two very different living environment. Living from the ocean into the land, we must first solve the problem of the body support. Biological buoyancy in the water than on land suffered in the air, so many creatures in the sea alive and kicking; to paralysis into a ball on the ground, and even the weight of their own can not load, beached whale is the best example. Because crabs have eight pereiopod already, so the fish than the terrestrial vertebrate ancestors, easier to _set_ foot on the land, the first step in a successful life. Although the sea water has a greater buoyancy, but because the crabs have eight pereiopod, just add a little more muscle power, can easily support the body on land. Of course, in addition to support and campaigns, to life on land; there are many problems to solve, such as loss of moisture, oxygen access problems. In addition; crabs there are some inherent physiological or other defects, resulting in the complete success of the obstacles to adapt to life on land. For these problems, all kinds of land crabs have a different solution, various methods have their advantages and disadvantages of course, differences in the results to show the merits of a crab in the degree of success to adapt to life on land.
Access of oxygen to adapt to life on land is land crabs a big problem. Most people have a misconception that the gills can only breathe in water, to the land to no avail. In fact, so long as to maintain contact with air and keep the surface moist and gill in the air as you can play the role of gas exchange, and oxygen in the air as the oxygen in the water nearly 50 times more efficient gas exchange, the smaller surface area to can achieve the same amount of gas exchange. Different land crabs in different ways to obtain oxygen on land, gills are usually very heavy and still play the role. General the number of land crab gill flap (Fig. 7) than in the aquatic crab gill flap (Figure 8) the small number of gill flap is also more rigid, and some species even in the gill flap between the structural support to prevent collapse of the gill flap in the air together, so long as the maintenance and humid, you can play a function in the air. In addition, many land crabs developed lung structure, can breathe air for gas exchange. Crab's lungs is different from the vertebrate lung, because the function of the same name. Land crabs of the lung is usually the inner surface of the gill chamber, a large number of blood vessels to the bottom of the film by the wet, where the crustaceans particularly thin, it can be swift and effective gas exchange. Some land crabs are a special way by another breathe on land, the author calls "the respiratory system of circulating water." These land crabs in all parts of the cheek area with a lot of fluff. When these land crabs on the surface activity, mainly by the gill chamber to breathe oxygen dissolved in water, the water through the gill chamber breathing crabs out of the water hole, it will be cheek area by the gravity flow to go under the body, the buccal area the formation of the hair will flow resistance, so that the formation of a thin layer of water film flow, gas exchange at this time work, the oxygen dissolved into the water, and carbon dioxide into the air, so that the water breathed again into the rich water containing oxygen, which oxygen-rich water; Finally, a large crab claws through the base of the hole into the water flow into the gill chamber, and then used for breathing crabs. Using this approach, crabs can be repeated use of the indoor water gill respiration. When the gills run out of room when the water evaporates, then enter the cave or water within the gill chamber of water added. These crabs will choose when the activities of high humidity, so may be in the air with a long active time.
Propagation:
Land crab has been the most completely adapted to terrestrial life, the fatal injury. The vast majority of land crabs usually totally unnecessary to have any relationship with the sea, but to reproduce, they were required to reproduce the seaside or to lay their eggs work. Since most of the land crab eggs hatched larva is only one of these larvae have been floating in the ocean of life, to other smaller marine plankton for food, after repeated shelling metamorphosis only after the change into a small crab, and then returned to life on land. Limited by the migration of the crabs, these crabs can not live too far from the sea, or in need of reproductive when they migrate over long distances. The origin of only a few freshwater land crab, eggs hatched out one by one directly to the small crabs, do not have anything to do with the sea, so you can live away from the sea inland. Most of these land crabs are still not too far away from the water, in addition to crab itself, the demand for water, the small crabs as small size, the water a lot more evaporation, more water needs to stay moist environment to live. In addition there are some crabs, the eggs hatched, though not small crabs, but that is a longer-end of osmoregulation larvae, so that the water in the crabs at the bottom of the cave; or living in some temporary water; such as snail shells , leaf water at the base, these crabs the crabs can not reproduce to the beach to lay their eggs.
In addition to the quantity of food, the food quality of the land crabs are also important. As the capacity of the stomach and digestive rate, land crabs processed foods per day is limited, so crabs will choose foods with high protein content, in order to increase access and improve nutrition, the growth rate. Therefore, crabs often prefer the green leaves of plants or branches in order to achieve better nutrition. However, if the plant has some toxicity, the land crabs will avoid eating the fresh leaves of these plants, and the litter of these plants for food. At this point of land crabs often choose some initial decomposition by microorganisms dry leaves, because such foods contain more microorganisms, have a higher protein content. In addition, some vertebrate feces and corpses for containing high levels of protein, crabs are often chosen as the target food. The lack of high-protein foods in place, land crabs there will be a final choice is to own the same kind of small crabs for food. This kind of the same type of small crab-eating behavior While this may seem cruel, but with even larger ecological significance, this behavior can reduce excessive competition within the species, and prevent the collapse of the whole population over a large, strong individual and can be produce more nutritious and better quality offspring, can improve the overall viability of the species.
The propagation of land crabs is a special thing. Many crabs have reduced the sea of collective behavior, spawning the female crab will be on the same day, with the release of hatchlings to the sea. This day is usually the full moon in the lunar calendar before and after 15, some species before and after the first day in the lunar calendar also has the crabs lay their eggs in behavior, such as medium-sized imitation of Sesarma. The most famous of collective land crabs breed in Australia, down the sea of red land crabs on Christmas Island, one hundred and twenty million of large land crabs after the start of the rainy season and then migrate to the sea to breed group, the crabs lay their eggs on the beach when the alarming number of clusters in each released into the sea nearly five trillion is only the crab larvae to the water near Christmas Island are stained red.
First, the land crabs land crab Branch is that people are most familiar with land crabs, also referred to the narrow sense of land crabs in the world, there are four genera and 17 species.
Second, the parties have crab crab families also belong to many species of land crabs, land crabs is a side can be regarded as a typical representative of crabs. The mainland is the world only four crabs.
Third, only about crabs in the sand crabs subjects some type of activity is not subject to tides.
(Photo: Tori Kogiku production) |
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