Cancer is an animal of the crustacean class. It is difficult to imagine a reservoir in which there would be no owner of a pair of powerful claws. And what a gambling hunt for crayfish can be! No, it’s not about banal fishing with the help of “rakolovka”, we are talking about a real fight, one on one. When you chase a barbel that is slipping away from you in a mask and fins (and where did all the talk about the clumsiness and slowness of crayfish come from?), And now, when it’s almost been possible to grab it, it quickly disappears into the hole ... In the heat of pursuit, not thinking about the danger , put your hand in there, and here it is - the moment of truth! I want to scream in pain, but you can’t ... and the cancer tightly gripped the fingers of its offender with its claws. The goal is achieved - the victim in the cage, but who caught whom, still needs to be figured out. However, we were somewhat carried away, because we need to start not from this. First, let's talk about what cancer is, what are its features. So, in this article we will consider the parts of the body of crustaceans, their lifestyle, and, incidentally, habits.
Recall the lessons of zoology: the structure of arthropods
Cancer is an invertebrate animal, its body is clearly divided into the front part - the fused cephalothorax, covered with brown-green and very durable shell; and the back is a segmented abdomen ending with a wide fin. On his head are two pairs of mustaches. The first short pair is the sense of smell. The second, long mustache, is responsible for touch. The eyes of the cancer are, as it were, set on the processes of the stalks; they can be pulled out with the help of muscles and pulled out. From above, the organs of vision are covered by the frontal spine-shaped processes that make up the anterior end of the cephalothorax. The oral cavity is surrounded by several pairs of jaw appendages of a very complex structure, due to which the food is finely ground before it enters the mouth. The lower part of the cephalothorax has five pairs of limbs. The first of these is large claws. With their help, cancer holds food in front of itself, and also protects itself from enemies. Claws are not used for walking. Cancer moves 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 with claws.
And what do they have inside?
The internal structure of crustaceans includes the following systems: digestive, circulatory, respiratory, excretory. The first of them has the appearance of a straight tube and, like all arthropods, consists of the anterior, middle and posterior ectodermal intestines. The circulatory system of cancers is an open type, that is, hemolymph flows through the sinuses and vessels of the myxocele. The heart is located above the intestines, in the dorsal part. The respiratory system of crustaceans is represented by gills, 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 altered whole foods. Cancer is an animal whose muscles are striated muscle tissue. He has no skin-muscle bag, the muscles are represented by separate large bundles.
Sexual separation
Females and males of crustaceans are slightly different in body structure. For example, males have large and powerful claws, their abdomen corresponds in width to the cephalothorax, and the anterior abdominal legs are well developed. Females have small claws, their abdomen is slightly wider than the cephalothorax, and the front legs are underdeveloped. However, these differences are visible only to the experienced eye. A man who understands crustaceans exclusively from a gastronomic point of view is unlikely to be able to distinguish a male from a female.
“The armor is strong and our tanks are fast”
As mentioned earlier, cancer is an invertebrate animal, but it has a strong chitinous exoskeleton. Its robust carapace provides reliable protection against enemies, however, it prevents the cancer from developing and inhibits its growth. Therefore, from time to time, crustaceans dump a hard cover (this process can be compared to molting). With great difficulty, the animal pulls legs and claws out of the shell, it even happens that they come off, but the lost limbs grow back. True, they differ in size and appearance. Reset of the shell lasts from several minutes to a full day. After that, the cancer becomes helpless and hides from numerous enemies. While its skin is covered with soft skin, the animal grows intensively in length. The curing of the shell is carried out within a month and a half. Shedding in young cancers occurs more often than in adults.
Living conditions
Crustaceans live mainly in the coastal zone, where they develop depths of up to three to five meters. They do not form continuous settlements; they concentrate on areas that are located on steep and steep shores composed of clay, silty, peat or sandy soil, in which it is very convenient to dig holes. Crayfish are very sensitive to the quality of water, as well as to the amount of oxygen dissolved in it. If the reservoir is contaminated with municipal wastewater and washes of agricultural pesticides (herbicides, insecticides, etc.), then crustaceans disappear from such waters.
Crustacean species
In our country, there are three main species: thick-toed, long-toed, and wide-toed crayfish. As their names indicate, they all differ only in the structure of the claws. Most often found are long-toed crustaceans. Individuals of this animal in various reservoirs may differ slightly in biology as well as in body structure. Often in the same water area only representatives of the same species settle, but there may be exceptions. Broad-toed crayfish are found mainly in the fresh waters of streams and rivers, as well as in clear lakes. This species of decapod crustaceans arranges settlement colonies on steep and steep banks. Thick-crayfish, on the contrary, practically do not live in fresh water bodies; they prefer brackish waters of estuaries and desalinated areas of the seas. And long-toed crustaceans are inhabitants of both brackish and fresh water bodies, they are less demanding of environmental conditions, therefore they are more common than other species. They can settle even in stagnant waters with a significantly lower oxygen content. As artefacts, these arthropod representatives use indentations between stones, under sunken trees, among the roots and stems of water plants. In addition, these cancers often bury themselves in silt, thereby distinguishing them from their broad-toed counterparts.