Cancer - pet class of crustaceans.It is hard to imagine a pond, which would not be the owner of a pair of powerful pincers.And what chance could be hunting for crabs!No, it is not a banal fishing with "rakolovok" we are talking about this fight, one on one.When stalking a mask and flippers to elude you barbel (and only where there was talk about the slowness and sluggishness crabs?) And that's when he almost managed to grab him, he quickly hides in a hole ... In the heat of the chase, not thinking about the danger, thrusting my hand, and here it is - the moment of truth!I want to scream out in pain, but you can not ... and cancer tightly clutched claws for fingers her abuser.Goal achieved - the victim in the cage, but who gets caught, still need to understand.However, we are a little carried away, because you need not start with that.First, let's talk about who is a cancer, what are its characteristics.So, in this article we will look at the body parts of crustaceans, their way of life, and of passing - habits.
recall the lessons of zoology: structure
Cancer arthropods - invertebrate animal, his body clearly divided into the front part - fused cephalothorax covered with brownish-green and very strong armor;and back - segmented abdomen, ending with a wide fin.On his head are two pairs of mustache.The first pair of short - is the olfactory organs.Second, long whiskers, are responsible for the sense of touch.The eyes of the cancer as if planted on shoots, stalks, they are using muscles may be made out and sucked in.Top of bodies covered by the frontal spinous processes that make up the front end of the carapace cephalothorax.The oral cavity is surrounded by several pairs of jaw appendages rather complex structure by which before reaching the mouth food finely frays.The lower part of cephalothorax has five pairs of legs.The first of them - a large claw.With their help, the cancer keeps the food in front of you and defend against enemies.To walk the claws are used.Moves cancer with the help of the so-called walking legs (the remaining four pairs).The ends of the first and second pairs contain rudimentary claws, and the third and fourth end in claws.
And what's inside?
crustaceans internal structure includes the following systems: digestive, circulatory, respiratory, excretory.The first of them is a straight tube and the like all of arthropods is composed of front, middle and rear ectodermal intestine.Circulatory system crayfish - non-closed type, ie hemolymph flowing sine and vessels miksotselya.The heart is located on the intestines, in the dorsal part.The respiratory system is represented by the gills of crustaceans, which are formed in a special cavity under the carapace.They are located in three rows.The excretory system is represented by the kidneys, which are mutated tselomoduktami.Cancer - animal musculature which is a striated muscle tissue.He had no skin-muscular sac, the muscles are represented by separate large beams.
sexual division
crustaceans Females and males are slightly different body structure.For example, the individual male have large and powerful claws, their abdomen is as wide as the cephalothorax, the anterior abdominal legs are well developed.Females have small claws, they belly a little wider than the cephalothorax, and the front legs are underdeveloped.However, these differences are noticeable only an experienced eye.But man, versed in crustaceans exclusively from the gastronomic point of view, unlikely to be able to distinguish male from female.
«Armor is strong and our tanks are fast»
As discussed earlier, a cancer - invertebrate animal, but it has a strong chitinous exoskeleton.His strong armor provides protection from enemies, but prevents cancer development and hinders its growth.Therefore, from time to time crustaceans shed their hard cover (this process can be compared to molt).With great difficulty the animal pulls out of the shell and claw feet, even it happens that they come off, but lost limbs grow again.However, while they differ in size and appearance.Reset shell lasts from a few minutes to a full day.After that, the cancer becomes helpless and hiding from enemies.While his body is covered with soft skin is, the animal is growing rapidly in length.The solidification of the shell is carried out for six weeks.Molt young crayfish occur more frequently than in adults.
Habitat conditions
They live mostly shellfish in the coastal area where the master depth of up to three - five meters.Continuum settlements they do not form, focus on sites that are located at the steep cliffs and composed of clay, silt, peat, or sandy soil, which is very convenient burrow.Cancers are very sensitive to water quality, as well as to the amount of dissolved oxygen.If the body of water is polluted municipal and industrial effluents and washings agricultural pesticides (herbicides, insecticides, and so on. N.), The shellfish disappearing from these waters.
crustaceans
In our country lives are three main types: thick-, and clawed crayfish.As the name suggests, they differ only in the structure of the claw.The most common clawed crustaceans.Individuals of the animal in various bodies of water may be slightly different as the biology and structure of the body.Often in the same water area settle only the representatives of the same species, but there may be exceptions.Shirokopalye cancers are found mainly in freshwater streams and rivers, as well as in clear lakes.This species of decapod crustaceans arranges settlement colony on the steep and steep banks.Thick-cancers, on the contrary, almost live in fresh water, they prefer brackish waters of estuaries and freshened areas of the seas.And clawed crustaceans are both inhabitants of brackish and freshwater, they are less demanding in terms of the environment, therefore more frequent than other types.They can settle even in stagnant waters with much lower oxygen content.As representatives of these shelters used arthropods deepening between stones under sunken trees, the roots and stems of aquatic plants.In addition, these cancers are often buried in the mud, thus they are different from their counterparts shirokopalyh.
