We answer the question about what characteristics are common to chordates

In this article we will consider in detail the question ofWhich features are common to chordates. Representatives of this type are distinguished on the basis of a number of characteristic features. We suggest that you familiarize yourself with the main ones.

So, which features are common to chordates? We start with two-sided symmetry. This sign is one of the most important.

Two-sided symmetry

All chordates are characterized by a bilateral(bilateral) symmetry. The same structure is characteristic of other types of multicellular animals, beginning with the lower worms. Two-sided symmetry reflects an important point in the evolution of multicellular. The transition to active movement in the environment is potentially associated with the intensification of nutrition and metabolic rate, the diversity of life forms and the expansion of the range of biotopes available for permanent habitation.

Secondary body cavity (whole)

The second major stage in the evolution of animals wasformation of the secondary body cavity (coelom). This stage begins with annelids. Biological significance of the secondary body cavity is associated with further activation of movement and nutrition. In the inattentive and primary-celiac animals, the intestine is surrounded by a loose parenchymatic tissue or liquid, the movement of food in the digestive tract is effected by contractions of the dermal-muscular sac, which simultaneously cause the progressive movement of the whole organism. In other words, the contractions of the entire trunk and intestine are synchronized, which biologically is not always beneficial for the effective assimilation of food.

The emergence of a secondary body cavity, whichdisconnects the intestines and skin-muscular sac, and the appearance of the own musculature of the intestine, formed from the mesoderm, opens the possibility of independent of the locomotion of intestinal motility. Each of these important functions - movement in space and digestive activity - is carried out depending on environmental requirements, does not limit each other. At the same time, the whole can play a supporting role, acting as a "hydroskeleton".

No less important is another function of the coelom -transport. Its outgrowth, penetrating deeply into tissues, ensures their supply with nutrients and oxygen. Based on the outgrowth of the intestine, the circulatory system is formed. The organs of excretion are connected with the whole. Thus, on the basis of the secondary body cavity, exchange at the tissue and organ level is maintained.

All chordates belong to the second-cavityanimals that phylogenetically connects them with such types as annelids, bryozoans, brachiopods, arthropods, echinoderms, pogonophores, etc. Secondary celiac originates from ancient coelenterates.

Secondary

which features are common to chordates and fish

Considering the common features of chordates(the subtype is cranial), it is necessary to note the secondary growth. All the secondary-cavity organisms break down into two branches: primary and secondary. The names of the groups are related to the peculiarities of embryonic development: in the former, the position of the oral opening corresponds to the blastopor, which is divided into the mouth and anus, while in the second blastopores it assumes the functions of the anal opening and the mouth breaks elsewhere. This group includes semihodovye, echinoderms, pogonophores and chordates. All other types of the secondary-living animals belong to the primary.

But the differences between these groups are moreare more important than the position of the oral opening. First of all, they differ in the nature of the formation of the coelom: in most of the primary, the whole is formed spasmodically (by splitting the mesenchyme), and the mesoderm arises by migration of cells from adjacent tissues (the teloblastic type) into this cavity. In the second-grained, the whole is enteroceous, it develops by paired protrusions of the intestine: their walls give rise to the mesodermal leaf. In addition, the primary moles are characterized by an unclosed circulatory system and a "ladder" type of the central nervous system, while in the second-averaged circulatory system is overwhelmingly closed, and the central nervous system has a different structure, in which large clusters of nerve cells often form in some places.

Specific features of chordates

In addition to the above features, characteristic of allchordate, but also found among other animals, representatives of the type of interest that we are interested in possess some specific features of the structure. The main of them will be discussed in detail later.

Chord

All chords have an internal axial skeleton,the main element of which is the chord. It is an elastic cord composed of vacuolated cells forming a cartilaginous tissue of the endoderm origin. Chord is surrounded by a sheath of connective tissue. Its main function is the supporting function; The axial skeleton helps maintain the shape of the body. A close relationship with the surrounding axial musculature and some degree of mobility, elasticity determine the chord's involvement in the lateral bends of the body, creating translational movement in a dense aquatic environment.

Chorda, as the only axial structureskeleton, exists only in the lower representatives of the type; in most vertebrates, it is laid in the embryonic period of development, but later replaced by the spine that forms in its connective tissue membrane. In biology tests, the question often arises: "What are the common signs for chordates and fish?". One of the correct answers is "the presence of a chord". In fish, the spine later assumes all its functions (including the locomotor system), and in terrestrial vertebrates it is mainly a supporting one; direct participation in locomotion is replaced by the function of support for individual parts of the motor apparatus.

Tubular structure of the central nervous system

Central nervous system in the form of a tube withthe cavity inside is a strictly specific feature of the chord type. Due to the fact that the nerve plate laid down from the ectoderm in the future embryogenesis is folded into the tube, a cavity is formed inside the spinal cord formed in this way - the neurocele (spinal canal) filled with cerebrospinal fluid.

We have not considered all the signs of chordates. We will tell about one more.

Gill slits

A characteristic feature of representativesThe type of our interest is that the anterior section of the intestinal tube of these animals is permeated with gill slits - the holes connecting the pharyngeal cavity (this section is called this) with the external environment. The appearance of gill slits is associated with the filtering nature of the food: through them water is released after the separation of food particles that enter the intestine.

Finally

So, we told about what signsare common for chordates. Based on them, as well as some other characteristics of representatives of this type are distinguished from others. It is necessary not just to memorize, but also to understand the common signs of chordates. The table below contains information about which subtypes and classes all its representatives share.