Vertebrate subtype (lat. Vertebrata) - the highest taxon of chordates, characterized by the most complex level of organization in the series of deuterostomes (insects are considered the top of protostomes). Another name for this group is cranial (lat. Craniota).
The taxon unites about 57 thousand species of animals, which is approximately 3% of their total number.
Main features of the vertebrate subtype
In terms of the level of morphophysiological organization, vertebrates are significantly superior to the lower chordates (tunicates and non-cranial). The main differential feature of this group is the presence of the spinal column and cranium (from which the name came). The notochord is present only at the stage of embryogenesis, during which all organ systems undergo significant complication.
Representatives of the vertebrate subtype are characterized by the following features:
- active foraging;
- differentiation of the neural tube into dorsal and cephalicdepartments;
- replacement of the chord by the spine;
- appearance of a head with highly developed sense organs;
- higher metabolic rate;
- presence of a heart and kidneys;
- complication of humoral regulation;
- development of the cranium that protects the brain and sensory organs located on the head;
- presence of a pharyngeal skeleton (visceral skull);
- complication of the central nervous and sensory systems;
- increasing the role of population organization and family groupings of individuals;
- complication of behavior;
- increased mobility, the appearance of paired limbs and their belts.
Among vertebrates, there are no representatives with a passive or "sedentary" lifestyle. These animals have spread widely across the Earth and occupied almost all ecological niches.
In order to assess the complexity of the anatomical and physiological organization of this group of organisms, it is enough to consider the structure of the most developed representative of the vertebrate subtype - man. Nevertheless, higher and more primitive lower taxa are also distinguished among cranials.
Taxonomic groups of vertebrates
Vertebrate subphylum includes 2 infratypes:
- Agnathans (Aghnata) includes 1 modern - cyclostomes.
- Gnathostomata.
Jaws include 2 superclasses: fish (Pisces) and tetrapods (Tetrapoda). The latter are divided into 4 classes: amphibians, reptiles, birds and mammals (the most highly organized taxon to which humans belong). signssubtype vertebrates form 2 different groups, one of which characterizes primary aquatic animals, and the other - primary terrestrial. In this regard, cranial animals are conventionally divided into anamnia (Anamnia) and amniote (Amnyota).
Systematic position
Vertebrates themselves in the animal classification system occupy the following position:
- kingdom - animals (Animalia);
- department - three-layer (Triploblastica);
- subdivision - deuterostomes (Deuterostomia);
- type - chordate;
- subtype - vertebrates.
Digestive system
The digestive tract of vertebrates consists of 5 sections:
- mouth;
- throat;
- esophagus;
- stomach;
- intestines.
Intestine, in turn, is divided into small, large and hindguts. The latter flows into the cloaca or ends with the anus. The ducts of the liver and pancreas exit into the first section, the presence of which is characteristic of all groups of vertebrates.
Body covers
Vertebrate skin consists of two layers:
- outer - represented by a multi-row epidermis arising from the ectoderm;
- internal - corium (otherwise the actual skin), is formed from the mesoderm.
The lower row of the epidermis is formed by actively dividing cells that replenish the upper layers. Various functional formations are concentrated in the outer part of the skin, including:
- glandular cells or glands (in higher cranial);
- scales, claws, feathers, hair, nails.
Color is caused by chromatophore cells located in both layers, containing accumulations of pigment.
Corium is formed due to the growth of connective tissue and is much thicker than the epidermis. This layer contains many blood vessels and nerve endings. Various protective formations can also form in the corium, such as bony scales and integumentary bones.
Respiratory system
Intensive metabolism of vertebrates is provided by highly efficient respiratory organs - gill apparatus (in anamnia) and lungs (in amniotes). The first can be represented by two types of formations:
- gill sacs - formed in cyclostomes;
- gill filaments - formed by folds of mucous membrane in aquatic gnats.
Gas exchange in the gills is based on the principle of countercurrent, which contributes to more efficient blood oxygenation. The lungs are bags that communicate with the pharynx through the larynx.
Additional gas exchange organs for some vertebrates are the skin, swim bladder and specialized outgrowths of the intestine.
Nervous system
Compared to the lower chordates, the vertebrate nervous system is highly differentiated. The brain includes the following departments:
- front (telencephalon);
- intermediate (diencephalon);
- medium (mesencephalon);
- rear (cerebellum).
The structure, degree of development and functions of each department in different classes of the vertebrate subtype differ significantly.
Vertebrate neurons form 2 types of matter:
- gray (consists of dendrites);
- white (formed by axons).
Axons are surrounded by an insulating sheath - a neurolemma, which ensures the independence of the passage of impulses.
The spinal cord can be of various shapes (a flat ribbon or a rounded cord). It is located in the canal formed by the upper arches of the vertebrae. There is a cavity in the spinal cord - neurocoel, which is surrounded by gray matter (white is located outside).
The brain and spinal cord form the central nervous system, and the nerves extending from them form the peripheral. The ganglionic system, centered near the spine, forms the autonomic nervous system, which is divided into sympathetic and parasympathetic.
Skeleton and musculature
Compared to the lower chordates, the vertebrate skeleton is significantly differentiated and includes 3 main sections:
- skull;
- axial skeleton;
- belts and their limbs.
In cyclostomes and cartilaginous fish, the skeleton is built entirely of cartilage. In other cranials, it consists of bones with a small proportion of cartilage.
Animals of the vertebrate subtype have 2 types of muscles:
- Somatic - is located under the skin and serves to carry out the motor activity of the body, formed by striated muscle tissue. Develops from dorsal mesoderm.
- Visceral - provides contractions of internal organs (digestive tract, blood vessels, etc.), represented by smooth muscles. Develops from the abdominal mesoderm.
Somatic musculature in lower vertebrates is segmented (except for paired fins and jaw muscles), while in higher vertebrates it is divided into separate groups that form different parts of the body (torso, head, locomotor organs, etc.).
Circulatory system
The circulatory system of vertebrates is closed and represented by three types of vessels:
- arteries (carry blood away from the heart);
- veins (carry blood to the heart);
- capillaries (small vessels branching in tissues).
The heart consists of striated muscle fibers that provide its intense contraction. In different groups of vertebrates, the cavity of this organ is divided into two, three or four chambers. In addition to the atria and ventricles, there are 2 additional sections - the venous sinus and the arterial cone.
Circulation scheme can be represented by one or two circles. Birds and mammals have the most efficient system in which 2 types of blood (arterial and venous) do not mix.
The blood of vertebrates contains the respiratory pigment hemoglobin, which carries oxygen, and formed elements (erythrocytes,lymphocytes, etc.).
Excretory system
The excretory organs of vertebrates are represented by paired kidneys, which remove excess fluid, s alts and products of nitrogen metabolism from the body. This organ has several varieties:
- pronephros (head kidney) - the most primitive type;
- mesonephros (truncal or primary kidney);
- metanephros (secondary or pelvic kidney).
From the blood to the kidney, products enter through the Malpighian canals, and into the ureters through the Wolffian.
Reproductive system
Reproductive organs are usually represented by paired ovaries or testes. Unlike non-cranial, vertebrates have genital ducts. In males, they are associated with the wolf channel, and in females, with the müllerian. The reproductive system of amniotes is more complex than that of anamnios.
