Our planet is very replete with various creatures, we have a wide variety of animals and plants. But in this work we will analyze in detail the type of arthropods. The general characteristics of these living beings will also be presented in the article.
Quantity
This is the largest and richest type in the animal kingdom. Representatives there are about a million species. Their number is one third of all living organisms on our planet, both living at a given time and extinct. Before we analyze the question "General characteristics of the type of arthropods" (7th grade of a comprehensive school is obliged to introduce children to its representatives), it is necessary to know that a large number of creatures still remain unexplored, their actual number theoretically can reach ten million or more.
They are distributed everywhere: in the seas, oceans, freshwater sources, on land. Based on which ecosystem a particular species has chosen, one canjudge evolution and food preferences. The type of arthropods, the general characteristic of which is our main task, is diverse, we propose to consider the classification for systematization.
Protection
We have already mentioned that the type has a large number of creatures, but despite such a variety, they all have a relatively similar body structure. Considering the type of arthropods (general characteristics), we note a similar feature - an external rigid skeleton consisting of chitin. Some species have an exoskeleton containing lipids, proteins, and calcium carbonate. This outdoor suit provides them with protection and body support. Also, the walls of the shell strengthen the muscles.
It is also important that all representatives are subject to molting, this process occurs due to the fact that the exoskeleton does not grow, and during the growth of the animal a bigger house is needed.
Body
The type of arthropods is rich and varied. The general characteristic also includes such a feature as segmentation. The whole body is divided into segments. Sometimes they grow together, in which case they are called tagmata, and the process is called tagmasis. One example is the fused head, thorax, and abdomen. Also, arthropods have processes with joints - that's where the name comes from, literally translated as "jointed legs".
Take the earliest and most primitive arthropods, then each segment of their body was associated with only one pair of appendages. However, most species have evolved, and the limbs have changed, other structures have formed,ex:
- oral apparatus;
- antennae;
- reproductive organs and so on.
Arthropod appendages can be either branched or non-branched.
Senses, gas exchange, blood circulation
Many representatives have well-developed sense organs (pair compound eyes), although some do not have this privilege. Their circulatory system is open, has no blood vessels.
Gas exchange occurs in several ways:
- gills;
- trachea;
- light.
Most arthropods are dioecious, usually fertilization occurs internally and eggs are laid.
Arthropod type: general characteristics, classification
These are symmetrical animals. It is also important to mention that they originate from annelids. If you analyze well, you can notice the similarity in structure. The only thing is that in the course of development and evolution, the first ones reached a high level of organization. Arthropods (general characteristics of the type, taxonomy and other issues will be discussed in detail) are divided into the following main classes:
- crustaceans;
- arachnids;
- insects.
In turn, each class is divided into squads. For example, among crustaceans, there are: cladocerans, copepods and decapods. Arachnids include: spiders, ticks and scorpions. And insects have a very large number of orders, suchlike:
- Orthoptera;
- dragonflies;
- Diptera;
- coleoptera;
- Hemiptera;
- Hymenoptera;
- Hypteroptera;
- fleas and many others.
Let's consider each class separately.
Crustaceans
This is a fairly diverse class, numbering about forty thousand species. Mostly they can be found in the seas and freshwater reservoirs, but there are some who have mastered the land.
Although the type of arthropods (a class of crustaceans, the general characteristics of which are discussed in this section) is very rich, a number of similar features can be distinguished, for this we will provide a table at the end of the paragraph to help systematize the knowledge gained.
They lead a floating, crawling or attached lifestyle. There are even parasites among them. As mentioned earlier, arthropods differ in body segmentation, there are from ten to fifty of them in this class.
Let's take a brief look at the characteristics of a typical representative of this class, the well-known crayfish. From the name it already becomes clear that he lives in fresh water. Its role in nature and for man is very great. Note that even outwardly male and female can be distinguished.
Activity is achieved at night, it feeds exclusively on plant foods, eating both live and dead prey. The size of a mature individual is from fifteen centimeters or more, they molt once a year, while in young animals this process is observed several times.once a year.
Like other representatives of arthropods, the circulatory system is not closed, the heart looks like a five-sided bag and is attached to the back wall of the body. It is also important to know that the head and torso are connected. Tactile and olfactory senses are sharp due to the long whiskers. The eyes are complex and attached to the flagella, which compensates for the immobility of the head.
| Signs | Characteristic |
| Departments | Two: cephalothorax and tail |
| Pair of mustaches | Two Pairs |
| Pairs of legs | Five pairs (ten legs) |
| Wings | Not available |
| Respiratory organ | Gills |
Arthropod type, arachnid class: general characteristics
As well as the previous one, it is very rich, has more than thirty thousand species of living beings, most of which live on land, but there are also secondary water representatives. Like crustaceans, they have a cephalothorax, in addition to this there is an abdomen. Note that segmentation is subject to change (some ticks do not have a segmented body at all, such as a dog).
The first segment of the body (cephalothorax) attaches six pairs of limbs to itself:
- Two pairs - jawbones.
- Four pairs of leg tentacles.
There are no limbs on the abdomen, but some representatives of this class have preserved lung sacs, sex plates or spider webs.
Another distinguishing feature of arachnids is the outer layer, consisting of lipoprotein, which protects the body from moisture loss. Most have venom and spider glands. As a rule, arachnids are predators, but a large group is made up of parasites and herbivores. Breathing is carried out with the help of lung sacs or trachea, but in spiders with the help of these two organs. The organs of sight, touch, smell and taste are quite well developed, but some ticks have no vision at all.
Fertilization occurs internally, live birth is observed in some species of ticks and scorpions. Although this class is quite diverse, but the most important units are:
- Spiders.
- Ticks.
- Scorpions.
Insects
Let's give a table reflecting the main features of insects.
| Sign | Features |
| Body | Head, chest, abdomen |
| Legs | Three pairs (six limbs) |
| Cover | Chitin |
| Breathing | Tracheae |
| Wings | Present in most representativesclass |
| Nervous system | Nodal |
| Circulatory system | Open |
This is the least studied class, but no less significant than the rest, it is poorly studied by science only because it is young.
