Arthropod animals with bilateral symmetry of the body: description, features

Approximately two-thirds of the species on Earth are arthropods. They live in fresh and salt water bodies, underground and on its surface, and many of them are able to move through the air. What are the characteristics of arthropods? Examples of animals, their description and features of the structure you will find in this article.

Who are the arthropods?

Arthropods - one of the most numerous and diverse groups in the animal kingdom. It includes about two million species. Their number is increasing every year due to the discovery of new species.

The list of arthropod animals includes crustaceans, arachnids, insects and centipedes. They inhabit all climatic zones of the planet, from the hot tropics, up to the regions of the Arctic and Antarctic. Representatives of this group live in deserts, forests, marshes, ponds and other ecosystems. Some of them feel comfortable in the homes of a person.

Since arthropods live practically in all environments and regions of our planet, their appearance and adaptations to the surrounding conditions are very different. Their sizes range from a millimeter to several meters. Meals also vary greatly. Some species are exceptionally predatory, others, on the contrary, are herbivorous. They can also be parasites, necrophagous (scavengers) or filtrates.

What do arthropods have in common?

They are so different that one wonders the question: why were they identified in one group? In fact, arthropods have common features. Their body and limbs are segmented and divided into divisions (tagmas), or segments. Why does the name take place.

In many species, the head and several divisions merge into one, forming a cephalothorax. The limbs extend from the lower side of the abdomen or the cephalothorax. They breathe lungs, trachea or gills. The circulatory system is not closed and enters the body cavity. They multiply by laying eggs or caviar. Larvae, as a rule, differ from adults.

Arthropods are animals with bilateral symmetry. Externally, the right and left halves of their bodies look the same. All of them have an external skeleton. It is a thin but strong cuticle made of chitin. It does not stretch, so as the animal grows, the animal dumps it to grow a new one. This process is called molting.

Centipedes

Perhaps, one of the most unpleasant groups of arthropod animals - centipedes. These include various species of scolopendra, common flytrappers, drupes, kivsyaks, etc. They are generally small (up to 10 cm), but some species grow to 35 centimeters in length.

Their name is fully justified, because millipedes have up to two hundred pairs of limbs. They prefer wet places and live in forests under the bark of trees, under moss, stones and fallen branches, but can live in dry and arid terrain. They are attracted by the bathrooms and the apartments.

During the day, animals hide in secluded corners, and at night they go hunting. Centipedes are predators. They feed on flies, cockroaches, spiders, fleas and other small animals. Sensing the danger, they turn into a ring, and glands on the back produce poisonous or intimidating agents: iodine, quinone and cyanide. For humans and domestic animals, their venom is not dangerous, if there is no allergy, then a little redness will remain from the bite.

Arachnids

The class of the Spider-shaped covers not only spiders, but also mites, saltpaws, scorpions, flagellates, false-scorpions, etc. Most of its representatives live on land, although some species of spiders and ticks live in water bodies. They are common in all regions of the planet, except Antarctica. Scorpions inhabit mainly areas with a warm or hot climate. Some spiders and mites live even in polar and circumpolar regions.

In the size of arachnids reach from a hundred microns (some mites) to 20-30 centimeters (scorpions, saltpigs, tarantula spiders). Their body is divided into the cephalothorax and abdomen. They are characterized by the presence of feetchips (pedipals), mouth jaws (chelicera) and four pairs of legs.

In scorpions, the second part of the body is elongated and resembles a tail. At the end of the "tail" is a small segment with a needle. It emits toxic substances. Their pedipals are enlarged and play the role of claws to capture prey.

Only spiders-horses and some species of ticks feed on plants. The rest of the arachnids are predators. They eat insects and small animals. Some catch prey, tracing it, others build traps in the form of cobwebs.

They paralyze the victim with a bite, so almost all are poisonous. Far from all the poisons are so powerful as to hit a person. Bites of black widows, arpiops, tarantulas, six-eyed sand spiders are considered dangerous.

Insects

Insects are the most numerous class of arthropod animals with bilateral symmetry of the body. More than one million species have been discovered. These are all kinds of beetles and butterflies, flies, ants, termites, cockroaches, moths, grasshoppers, etc.

The main feature of many insects in comparison with other arthropod animals is the ability to fly. Dragonflies and some flies develop speeds of up to 15 meters per second. Those insects that do not have wings, run or move with jumps (fleas, grasshoppers).

They live in completely different environments, even in water. Some live there the whole of their life (waterfowl, whirligigs, bedbugs, waterers), others - only a certain period in development (dragonflies, caddis flies, water birds). Their limbs are modified in such a way that they allow animals to slide freely over the surface of the water.

Insects live alone or in groups. They feed on both plant and animal food, dead organisms and animal residues. In search of food, they can overcome hundreds of kilometers per day (locusts).

Public insects can be combined into large groups, within which there is a clear hierarchy and division of responsibilities. So, for example, live ants, bees, termites, bumblebees.

Crustaceans

The group of crustaceans covers more than 70 thousand species, among which there are crabs, crabs, shrimps, lobsters and other animals. Most of them inhabit fresh and salt water. Crumbs and some crabs prefer wet land areas.

All crustaceans have two pairs of antennae (antennas and antennas), and their limbs are bifurcated at the ends. They breathe mostly by the gills. In some representatives, gas exchange occurs throughout the body surface. Sea ducks and sea acorns lead an immobile way of life, attaching themselves to rocks, stones and other surfaces.

On the nature of food, many crustaceans are filtrates. They eat small organisms, such as plankton, detritus. In addition, eat dead animals, clearing ponds. Crustaceans themselves are food for fish and aquatic mammals.

Man also uses them for food. In countries near the sea, crustaceans occupy a large share of the fishery. A sea duck is considered one of the most expensive delicacies in the world.