Shrimp and lobsters, lobsters and crabs.The wonderful world of creatures that were more than five hundred million years ago.On them will be discussed in the article.You will also see in the photo crustacean giant size, scope limbs which reaches four meters.
When studying the lessons of the class of Crustaceans, table of the main features of these creatures are often given at home.After reading our article, any student can easily reach it.
What Crustaceans
One of the largest groups phylum Arthropoda - Crustaceans.It includes more than seventy three thousand species.And the oldest member of this group of researchers called Szczytno.Its modern structure completely identical to fossils, which are more than 200 million years.
feature of this subtype is that it also includes a transition stage from plant to animal world.These are the barnacles and barnacles.They did not move.Among other crustaceans and woodlice worth noting some crabs, which do not live in the water and on land.Amphipods live in moist tropical soils of our planet.There is even a kind of parasite - taxa.
Thus, this biological subtype mastered almost all the options of reservoirs of the Earth, from the seabed to the river banks.
Next we'll look at the main representatives.You will see a gigantic crustacean and learn about the small crustaceans, body size is only 0.1 millimeter.
All kinds of living beings on our planet is studying biology.Crustaceans are the responsibility of such disciplines as carcinology.
Among the important distinguishing features of this subtype is called the carapace, or chitin exoskeleton.This solid parts of the body of crustaceans, which protect them from external mechanical influences.As the exoskeleton is not increased in size, the animals have to reset it several times in life is to continue its growth.
They also have two pairs of antennae and they breathe with the help of gills that are located on the legs.
For more information about the external and internal structure of the crustaceans will be discussed later.Now it is important to note one thing.This biological subtype is the most important link in the food chain.Users, for example, uses a lot of shrimp.Therefore, nature provides a large number of representatives of this class.
Krill, for example, and copepods, which we discuss later in the article, have the largest biomass of all the species on Earth living beings.
So, let's get acquainted with the structure of crustaceans.
external structure
subtypes phylum arthropods, crustaceans have an external chitin (or lime) carapace and a segmented body surface with different numbers of paired limbs.
the smallest group considered tantulokaridy.Their size varies from 0.1 to 0.3 millimeters.This is also the parasite - the smallest crayfish Stygotantulus stocki, mentioned above.Its size is around 94 microns (less than 0.1 mm).
largest representatives reach a weight of twenty kilos and scope of the forelimb of 3.5 - 3.8 meters.With regard to this kind of crustacean appeared a mystery, "a crab can hug a hippo?" This is the Japanese spider crab, which we will discuss below.
external structure of crustaceans roughly the same in all species, but different number of segments and the appearance of the legs at different stages of the life cycle.
So, headache, abdominal and thoracic present in all members of this subtype.However, in some underdeveloped crustaceans segmentation of the latter two departments homonomous.That is, the surface of the body is divided into parts of equal size.
In higher crayfish, which we will talk a little later, a permanent segmentation.It consists of four parts: abdomen, consisting of six segments, the cephalothorax, which has four head and eight thoracic segments, and Akron (special area near the mouth of the head, there is only in arthropods).
limbs of crustaceans are located on separate segments of the body in pairs.Speaking the language of science, the "leg" consists of protopodite (basic course) which includes koksopodit (here are the gills) and basipodite (connecting part) and two sequels - and exopodite endopodite.
functions from different limbs, basically they vary depending on the type of crustacean.Some are breathing, while others - for the movement, or a meal, the higher the use of all the functions without exception.
Internal structure The internal structure of crustaceans consists of five systems, muscles and sensory organs.Study it, we'll start with muscle.
So as representatives phylum Arthropoda, crustaceans musculature represented striated muscle tissue.Overall they do not have a bag, and the muscles are located, if the individual beams.They generally serve as a link between the different segments of the body surface.
circulatory system in this subtype open.That is, blood and lymph united and move sine miksotselya and vessels.It is noteworthy that the heart is always located near the respiratory system.It turns out that it is different from individual representatives of crustaceans.Some of this organ is the gut, in others it is a tube the full length of the body.Each compartment of the latter have special holes for distribution of blood in the segment.There are hearts in the form of a bochonochka ostiyami.Thus, this body of representatives from different subtypes can be longer or shorter.
nervous system is primitive and more developed crustaceans.At first she was "ladder", the second a whole, many sectors which have merged.The first type is characterized by spaced sides ganglia, which are connected by commissures.The brain consists of crustaceans deytotserebruma which has a connection with antennules and prototserebruma responsible for eye, Akron and antennas.
nervous system in some species closely related to the endocrine.With this certain crustaceans can change the color of the body and to better adapt to the environment.
respiratory system also varies depending on the evolution of the species.So, the least developed crustaceans breathe the entire surface of the body by passing the water through a special system.Landlubber got a special body - psevdotraheyami - but for the life they need moist air only.The respiratory system is the main mass of crustaceans is epipodite, special gills that are located on the front of the abdominal or limb.
digestive system takes the form of the tube and consists of three gut - front, middle and rear.Milling substances occurs in the anterior, absorption and digestion of - on average, and the output - through the rear.
excretory system consists of a pair of kidneys.In general, these bodies are of two types - antennal and maxillary.Some crustaceans are born with the first type of kidney disease, in the process of replacing it with a second life.And vice versa.All four bodies there is only one species of higher crayfish - Nebalia.
Senses presents well-developed eyes statocysts (organs of balance) and special hairs on the antennae, that provide the sense of smell and touch.
life cycle
Next to continue our characterization of crustaceans description of their life cycle.It begins with the embryonic period.It all depends on the amount of deferred yolk eggs.
If it is small, which is normal for underdeveloped representatives subtype, the division is exactly the same as that of the annelids.That is all part of getting an equal amount of matter and at the end of embryonic development appear identical beings.
Otherwise, the higher crustaceans, eggs yolks much, so separation is superficial.They formed the germ band, which later forms the whole process of development.
After that there is hatching from an egg.The larva of crustaceans called "nauplius."He has Akron antennules couple swimming dvusegmentnoe limbs and body.The following stages are found only in higher crustaceans.
zoea - a period of development, when larvae appear eyes, abdomen and limbs on the head and front of the chest.
The next stage is called larva mizidnaya.She fully formed limbs of crustaceans and all the senses with the systems of the body.In the process of increasing the size of it several times molts, shedding cuticle.For more information about this metamorphosis will be discussed later.
Molting is regulated at the level of hormones.During the growth of the being comes a certain stage when the old shell prevents further development.Due to the signal from the hypodermic organism begins to form an increased supply of nutrients.With it formed a new layer of the cuticle.After bursting old and no longer young crustaceans surface hardens rapidly due to mineral salts.
is noteworthy that the growth of cancer occurs in two stages.Prior to molt the increase in cell number, and after that - a set of water in the tissue.
There are also some species of crustaceans, which change the size, the length of the limbs and organs, depending on the seasons.
Contact ecology
Then our response crustaceans affect lifestyle and distribution.
Scientists compare the representatives of this subtype in the reservoirs of insects on land.They are also many kinds, shapes, sizes, and their number is just a huge biomass.
During evolution there was a division in the elementary and higher crustaceans.Some became parasites, some were able to adapt to life on land and have developed specific respiratory system.
Regarding parasitic forms, they exist in various groups of this subtype.The main feature of this part of the crustacean is a maximum simplification of the different organs and systems.Because they live at the expense of others, many parts of the body will atrophy just as useless.There are those that parasitize within the various living beings, but there are those that are attached externally.
noteworthy that representatives of this subtype can be found everywhere.Small mind living in puddles, melting snow and salt marshes.Large shellfish also are both at depth and along the coast of the sea, lake or river.
Smaller representatives of this subtype, predominantly related to the plankton, feed on bacteria and protozoa organisms.Other crustaceans that live on the bottom of ponds, feeding on carrion.They settle down pieces of the flesh of dead animals from the higher layers.Dead bodies of the same, which are on the surface or in shallow water, feeding on amphipods.
addition, shellfish are an important target species.Shrimp, lobster, crayfish, crabs, crayfish - is only part of the names of species, which are used by people as food.For example, the barnacle, or bloody fingers are on the Iberian Peninsula up to 150 euros per kilo.
second application crustaceans - as food for fish and birds, which are grown on the farm.Aquarists also use them in dried fish food.
also used the ability of shellfish absorb carrion.They are used for the natural purification of water bodies from pollution.
malacostraca
in biology class is usually studied class of crustaceans.Table distribution, structure, life cycle.All these questions you've easily give an answer on the basis of the previous article.
Now let's move on to the more advanced group of beings.Next we visit the world of these amazing creatures, look at his giants and dwarfs.In the meantime, you should get the general information about this class.
malacostraca include more than thirty-five thousand species of living beings.The first members of this class have appeared in the Cambrian period.And it was about five hundred and forty million years ago.It includes crabs, amphipods, crabs, shrimps and woodlice.These beings living in sea and fresh water and on land.
structure of higher crayfish is somewhat different from the less developed counterparts.At their head is formed as a result of accretion sintsefalon the first three segments.The forelimbs are transformed into maxilliped, the better to receive the food.Additionally, they produced two-chambered stomach.
Now let's take a closer look with the individual members of this class.Next, you will learn the most common names of crustacean habitat, structure and methods of their use by man.
Also, you will be presented crustacean giant size, the scope of the forelimbs, which reaches three and a half meters.
So, what is this giant crab?
largest representatives
«Giant Crab" is known in many cultures of the world.Today we talk about the real, not the legendary representatives of this class.
So the first crustacean gigantic proportions in our list - it is the Tasmanian crab.Individuals of this species reach a weight of thirteen kilos.Carapace they happen to half a meter in width.He lives on yuzhnoavstraliyskom offshore, at a depth of one hundred to three hundred meters.It feeds on everything that moves slower than him.Starfish and gastropods constitute the bulk of the diet.
Next Giant - king crab.This king crab from the hermit crabs.Previously found only in the Far East.But in the seventies it was able to move into the Barents Sea.Now, these crabs are found off the coast of Norway and Svalbard.
After they settled down in a new place, Kamchatka crabs began to multiply rapidly and destroy local fauna.In addition, they are large enough.The length of the swing limb reaches one and a half meters, and the weight of males - up to eight kilograms.These two factors have influenced the fact that these crabs have been the object of fishing.In the year of their catch more than twelve tons in Russia.
But the champion, which undoubtedly boasts the class of Crustaceans, this Japanese spider crab.Its shell, as well as in the previous, about half a meter wide.But the scope of the extremities up to three - three and a half meters.The weight of the largest fish can be up to twenty kilograms.Estimated lifetime - about a century.
Is found this giant off the coast of Japan, at a depth of up to three hundred meters.While some individuals have seen and eight hundred meters under water.
used this type of shellfish, not only in food but also in decorative and scientific purposes.
Freshwater crayfish
Besides sea of the class, such as crab, lobster and lobster crustacean creature can live in fresh water.Among the most common species is the following: the river shirokopaly and signal crayfish.
first one was, until recently, very common in virtually all bodies of water in Europe.But due rachey plague and importation of American type of individuals he quickly began to fade.
size shirokopalyh cancers hovers around twenty centimeters.The color is from green to brown and brown with a blue tint.It is noteworthy that they just settle in clean waters.If they are not in the nearest river or lake, then chemically contaminated area.
Class Crustaceans has a fitted look.Signal crayfish slightly smaller than its European counterpart, but differs vitality and better adaptation.
feed on crayfish detritus.It settled on the bottom of the reservoir remains of the dead living things and their secretions.
signal crayfish is found today in more than twenty-five European countries.In Russia it is known only in the Kaliningrad region.
problem of the coexistence of these two types is that the American crawfish are not affected by the fungus causing Hrachya plague, but they are the carriers of other infections.Therefore, their appearance in the pond probability of survival in it shirokopalogo cancer tends to zero.
crabs, lobsters, shrimp
marine crustaceans, unlike the river, more diverse.The most popular in the fishery considered crabs, crayfish, lobster, shrimp, and other species.
Now we'll talk about them a little more.
Good luck to you, dear readers!
