The earth is made up of three parts of water and one part of land. There is a large variety of plants, animals and other species living on the land. The different types of flora, fauna and living organisms make the land distinct and colourful. Even the marine regions of the earth have a varied species of fish, molluscs, reptiles, mammals, etc.
The marine ecosystem also has many plant and animal species which are very unique and wonderful. The crab is one among those wonderful creations which add on to the beauty of marine ecosystem. Crabs are the crustaceans which can survive both on land as well as in the sea. There are different types of crabs like hermit crab, king crab, horseshoe crab, etc. Crabs have a flat body and can breathe under the water as well as on the land. The crabs don’t have a nose or any such openings for breathing. This gives rise to a very interesting question: how do the crabs breathe?
Like the fishes, crabs also have gills in their body. Over the top of a crab’s body, there is a flat gill which is responsible for the breathing process in crabs. These gills are located on the top of walking legs of the crab. When the crab enters the water, the gills become moist, absorbs the oxygen from the water and the oxygen molecules directly come in contact with the blood of the crabs.
When the crabs move to the land, there is no water to make the gills moist. But these gill have already stored moisture in them. This moisture is used during the process of respiration. The oxygen in the atmosphere comes in contact with the moisture in the thin gill of the crabs and thus enters the body of the crab. This is how the crabs get oxygen for their respiration process.
The process of breathing is not the same for all the crabs. Crabs are generally divided into three categories – the aquatic crabs, the intertidal crab and the terrestrial crab. All these crabs have different levels of comfort inside and outside water. The aquatic crabs are the first category of crabs. As the name suggests, these crabs are found mostly under the water. If they stay outside water for a long time, the moisture stored in the gills is lost resulting in collapsing of the gills.
The intertidal crabs can breathe easily both in water as well as on land. When in water, the gills help in respiration. On land, the cuticles near the legs of crab help in the absorption of oxygen. The terrestrial crabs are more likely to stay on land. Their gills are very stiff which makes it more comfortable for them to stay on land. If kept in water for a long time, the terrestrial crabs will die.
The crabs can even collect water from the dew or puddles. Though they don’t have the nose to breathe but the gills and the cuticles containing moisture are responsible for the survival of the crabs. This is indeed the only reason for crabs hiding in the dark areas so that the evaporation of moisture can be reduced to minimum. Thus, this amazing creature is alive only because of the unique way of respiration of their body.