Chordates are animals that have a complex structure and variety

Chordates are the most highly organized creatures from all the representatives of the kingdom of Animals. The characteristic features of the structure allowed them to become the pinnacle of evolution.

Signs of Chordates

The main features of these animals are the presence of a chord, a neural tube and gill slits in the pharynx. Chordates are organisms in which the listed features can be significantly modified.

So, the skeleton can be external and internal. And the development of chordates in ontogenesis can be characterized by the fact that the gill slits are overgrown even in the embryonic development of organisms. At the same time they develop other respiratory organs - air bags or lungs.

Axial skeleton

The main characteristic of chordates is the presence of a chord. It is an internal axial skeleton, which in the form of a single strand passes through the entire body. Throughout the life of the chord, not many representatives of this type remain. These include different types of lancelets, representing the class of the Holovochord subtype invertebrates.

The rest of the chord develops into a skeleton. Only a few of them consist of cartilaginous tissue. Bony fishes, amphibians, reptiles, birds and mammals have a completely ossified skeleton. In the process of evolution, it becomes more complicated. Its components are the skull, spine, thorax, belts and immediately upper and lower extremities.

Gill slits in throat

Chordates are animals in which the organs of the respiratory system are formed as outgrowths of the pharynx. This is their main difference from invertebrates. In this group they are derived from the limbs.

Of course, this anatomy is not all chordates. Gill slits are preserved in the lancelet and cartilaginous fishes: sharks and rays. In animals that are adapted to breathing atmospheric oxygen, they are overgrown in the early stages of embryonic development. After the lungs are formed.

Features of the nervous system

The system, which ensures the interrelation of the organism with the environment, in chordates is initially formed as a neural tube. It has an ectodermal origin.

Chordates are highly developed animals, largely due to the peculiarities of the structure of the nervous system. Thus, in mammals it is represented by the spinal cord located in the canal of the spine, and also by the head. They are parts of the central nervous system. The brain is securely protected by the bones of the skull, which are fixed together. It is differentiated into departments according to a functional feature. Anatomically, through the hole formed by the vertebrae, the brain is connected to the spinal cord. The peripheral part of the system is formed by the spinal and cranial nerves. They serve as a "transport highway", combining a complex organism into a single whole and coordinating its work.

The structure of the nervous system determines the complex behavior of chordates, the formation of conditioned reflexes and a clear program of instinctive behavior.

A variety of chordates

This type includes three subtypes: Cranial, Larva-chordate (Shell) and Cranial (Vertebral).

The first of these concerns only 30 species that occur in our time. Their representatives are lancelets. These animals outwardly resemble a surgical instrument called a lancet.

The body of these small animals is almost always half in the sand. So it is more convenient for a lancet to filter water by swallowing nutrient particles.

The most numerous subtype of chordates are Vertebrates. They have mastered absolutely all habitats, filled food chains and ecological niches.

The aquatic inhabitants are fish. Their body is streamlined in shape, covered with scales, they are adapted to the gill respiration, they move with fins.

The first to go to the land are amphibians. These are frogs, toads, newts, worms and fish. Their common name is due to the fact that they live on land, breathe with the help of light and skin, but the process of their reproduction occurs in the water. Like fish, their females are rushing into the water caviar, which males are watered with seminal fluid.

Typically terrestrial animals are reptiles. Lizards, snakes, turtles and crocodiles spend only time hunting in the water. They multiply by eggs, which are deposited in special shelters on land. Their skin is dry, covered with dense scales.

The last sign was inherited from reptiles. The uneven part of their feet is called a pike. It is she who is covered with small scales. This fact scientists consider as evidence of origin in the process of evolution. Birds are capable of flying thanks to many features of the external and internal structure. This is a modified front limbs, feather cover, a light skeleton, the presence of a keel - a flat bone, to which the muscles are attached, propelling the wings.

Finally, the Beasts, or Mammals, are the crown of evolution. They viviparous and feed the cubs with milk.

Chord animals are the most complex, diverse in structure, playing the most important role in nature and human life.