– to watch one of the best entertainments for the person having a rest on the beach by the sea crabs. These representatives of a class of Crustacea amuse people with the usage to move not forward, and sideways.
The question of the reasons of such way of movement of crabs and also of why crayfish move back back, occupied people still in the ancient time. Even the legend of how a crab and cancer accompanied the sea tsar on walk, and at a meeting with a shark cancer was born, having been frightened, recoiled back, and the crab sideways departed in the closest thickets of seaweed. The sea tsar punished both citizens for cowardice, having forced one all life to move back, and another – to go sideways.
Certainly, the modern person will not accept such fantastic explanation.
Anatomy of a crab
Crabs possess very long and powerful legs which are a little twisted forward. Thanks to it joints cannot rise above a paunch. It is very important for the animal who is spending the most part of time for shallow water and having many natural enemies. In case of danger it is easy for crab to sprawl at a sandy bottom, without drawing attention, or to hide quickly under stones.
But the crab should pay for the similar structure of extremities with the fact that he can gather the largest speed at the movement side. When speed is not critical, the crab can go in any direction, but having felt danger, he seeks to escape and begins to move the most convenient for it in the way. It does not prevent to watch a danger source, eyes at it are on pedicellate outgrowths that creates the circular review. There is also one more reason for movement by a side in case of danger. Claws at a crab, as well as hands at the person, are asymmetric – easy to make sure of it, having looked at it: one of claws is larger another. As well as people, conducting at the majority of individuals have the right claw, the crab captures by it food, and left he if necessary is protected. Running away from someone dangerous, he is covered with a "protective" claw, and too it is more convenient to do it, moving sideways.
Cancer moves back back
The interesting feature of movement is available also for close "relative" of crabs – a crawfish. This animal swims a tail forward as in such direction the body of cancer has the most streamline shape, and at the movement in an opposite direction would stir big claws. Cancer can go in any direction, but gathers the maximum speed at the movement back to front. The tail at the same time is bent under a paunch and throws out a water jet which "works" by the principle of the jet engine, increasing the speed of movement of an animal. Not always the crab goes sideways, and cancer moves back back – both act this way only in case of danger. Animals perceive a meeting with the person as danger therefore people most often observe such movement of crabs and crayfish.