About two-thirds of the species on Earth are arthropods. They live in fresh and salty water bodies, underground and on its surface, and many of them are able to move through the air. What are arthropods characterized by? Examples of animals, their description and structural features can be found in this article.
Who are arthropods?
Arthropods are one of the most numerous and diverse groups in the animal kingdom. It includes about two million species. Their number is increasing every year in connection with the discovery of new species.
The list of arthropods includes crustaceans, arachnids, insects and millipedes. They inhabit all the 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, swamps, ponds and other ecosystems. Some of them feel comfortable in people's homes.
Since arthropods live in almost all environments and regions of our planet, their appearance and adaptations to environmental conditions are very different. Their sizes range from a millimeter to several meters. Meals also vary greatly. Some species are exclusively predatory, others, on the contrary, are herbivorous. They can also be parasites, necrophages (scavengers) or filtrates.
What do arthropods have in common?
They are so different that the question involuntarily arises: why were they identified in one group? In fact, arthropod animals have common features. Their body and limbs are segmented and divided into departments (tags), or segments. That is why the name comes about.
In many species, the head and several departments merge into one, forming the cephalothorax. The limbs extend from the underside of the abdomen or cephalothorax. They breathe in the lungs, trachea or gills. The circulatory system is not closed and enters the body cavity. They breed by laying eggs or eggs. Larvae, as a rule, differ from adults.
Arthropods are animals with bilateral symmetry. Outwardly, the right and left halves of their bodies look the same. All of them have an external skeleton. This is a thin but durable cuticle of chitin. It does not stretch, so as the animal grows, it drops it in order to grow a new one. This process is called molting.
Millipedes
Perhaps one of the most unpleasant for humans groups of arthropod animals is millipedes. These include various species of scolopendra, common flycatchers, drupes, kivsyaki, etc. They are mostly small (up to 10 cm), but some species grow up to 35 centimeters in length.
Their name is fully justified, because millipedes have up to two hundred pairs of limbs. They prefer moist places and live in forests under the bark of trees, under moss, stones and fallen branches, but can live in a dry and arid area. They are also attracted by the bathrooms of the apartments.
During the day, animals hide in nooks, and go hunting at night. Millipedes are predators. They feed on flies, cockroaches, spiders, fleas and other small animals. Sensing danger, they curl up into a ring, and glands on their back secrete substances that are poisonous or frightening for opponents: iodine, quinone and hydrocyanic acid. For humans and domestic animals, their poison is not dangerous, if there is no allergy, then only a slight redness will remain from the bite.
Arachnids
The class Arachnids covers not only spiders, but also ticks, salpugs, scorpions, flagella, 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 ticks live even in the polar and circumpolar regions.
In size, arachnids reach from hundreds of microns (some ticks) to 20-30 centimeters (scorpions, saltpugs, tarantulas). Their body is divided into the cephalothorax and abdomen. They are characterized by the presence of leg tentacles (pedipals), oral 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 releases toxic substances. Their pedipals are enlarged and play the role of claws to capture prey.
Only horse spiders and certain species of ticks feed on plants. The remaining arachnids are predators. They eat insects and small animals. Some catch prey, tracking it, while others build traps in the form of a web.
They paralyze the victim with a bite, so almost all are poisonous. Not all poisons are so strong as to hit a person. Bites of black widows, argiop, tarantulas, six-eyed sand spiders are considered dangerous.
Insects
Insects are the most numerous class of arthropod animals with bilateral body symmetry. Over one million species have been discovered. These are all kinds of bugs and butterflies, flies, ants, termites, cockroaches, moths, grasshoppers, etc.
The main feature of many insects in comparison with other arthropods is the ability to fly. Dragonflies and some flies reach speeds of up to 15 meters per second. Those insects that do not have wings run or move in leaps (fleas, grasshoppers).
They live in completely different environments, even in water. Some live there all their lives (swimmers, swivels, water-bugs), while others live only for a certain period in their development (dragonflies, caddis flies, water-lovers). Their limbs are modified so that animals can freely slide on the surface of the water.
Insects live singly or in groups. They feed on both plant and animal food, dead organisms, and animal debris. In search of food, they are able to overcome hundreds of kilometers a day (locusts).
Social insects can be combined into large groups, within which there is a clear hierarchy and separation of duties. So, for example, ants, bees, termites, bumblebees live.
Crustaceans
The group of crustaceans covers more than 70 thousand species, among which there are crayfish, crabs, shrimps, lobsters and other animals. Most of them inhabit fresh and salty water bodies. Woodlice and some crabs prefer wet land.
All crustaceans have two pairs of antennae (antennas and antennae), and their limbs are bifurcated at the ends. They breathe mainly by gills. In some representatives, gas exchange occurs throughout the surface of the body. Sea ducks and sea acorns lead an immobile lifestyle, attaching to rocks, stones and other surfaces.
By the nature of their nutrition, many crustaceans are filtrates. They eat small organisms such as plankton, detritus. In addition, they eat dead animals, cleansing ponds. Crustaceans themselves are food for fish and aquatic mammals.
Man also consumes them as 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.