Vertebrata subtype (lat. Vertebrata) is the highest taxon of chordates, characterized by the most complex level of organization in the series of secondary cirrhotids (insects are considered the top of the primary cirrhotic). Another name for this group is cranial (lat. Craniota).
The taxon unites about 57 thousand species of animals, which is about 3% of their total number.
The main signs of a vertebrate subtype
In terms of morphophysiological organization, vertebrates are significantly superior to the lower chordates (tunicans and cranium). The main differential feature of this group is the presence of the spinal column and cranium (from which the name came). The chord is present only at the stage of embryogenesis, during which all organ systems undergo significant complication.
Vertebrate subtype representatives are characterized by the following features:
- active food search;
- differentiation of the neural tube into the dorsal and head sections;
- replacement of the chord by the spine;
- the appearance of a head with highly developed sense organs;
- higher metabolic rate;
- the presence of heart and kidneys;
- the complication of humoral regulation;
- development of the cranium protecting the brain and sensory organs located on the head;
- the presence of the pharyngeal skeleton (visceral skull);
- complication of the central nervous and sensory systems;
- the increasing role of the 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 spread widely throughout 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 - the human being. Nevertheless, among the cranial, higher and more primitive lower taxa are distinguished.
Taxonomic groups of vertebrates
The vertebrate subtype includes 2 infratypes:
- Jawless (Aghnata) includes 1 modern - cyclostomes.
- Maxillary (Gnathostomata).
The mandibular 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). The signs of the vertebrate subtype form 2 different groups, one of which characterizes primary aquatic animals, and the other primary primitive. In this regard, the cranial are conditionally divided into anamniya (Anamnia) and amniot (Amnyota).
Systematic position
Vertebrates themselves in the classification system of animals occupy the following position:
- kingdom - animals (Animalia);
- department - three-layer (Triploblastica);
- subdivision - secondary (Deuterostomia);
- type - chordates;
- subtype - vertebrates.
Digestive system
The vertebral digestive tract consists of 5 sections:
- mouth;
- pharynx;
- esophagus;
- stomach;
- intestines.
The intestine, in turn, is divided into small, large and hind gut. The latter falls into the cesspool or ends with the anus. The ducts of the liver and pancreas, the presence of which is characteristic of all groups of vertebrates, enter the first section.
Integument
The skin of vertebrates consists of two layers:
- external - represented by a multi-row epidermis arising from the ectoderm;
- inner - corium (otherwise the skin itself), is formed from the mesoderm.
The lower row of the epidermis is formed by actively dividing cells that replenish the upper layers. In the outer part of the skin, various functional formations are concentrated, including:
- glandular cells or glands (in higher cranial);
- scales, claws, feathers, hair, nails.
Color is determined by chromatophore cells located in both layers, containing accumulations of pigment.
The corium is formed due to the growth of connective tissue and significantly exceeds the epidermis in thickness. There are many blood vessels and nerve endings in this layer. Various protective formations, such as bone scales and integumentary bones, can also form in the corium.
Respiratory system
Intensive vertebrate metabolism is provided by highly efficient respiratory organs - the gill apparatus (in history) and the lungs (in amniot). The first can be represented by two types of formations:
- branchial bags - formed in cyclostomes;
- gill lobes - formed by folds of the mucous membrane of the aquatic maxillary.
Gas exchange in the gills is based on the principle of counterflow, which contributes to a more efficient oxygen saturation of the blood. The lungs are bags that communicate through the larynx with the pharynx.
Additional organs of gas exchange for some vertebrates are the skin, swim bladder and specialized outgrowths of the intestine.
Nervous system
Compared with the lower chordates, the nervous system of vertebrates is highly differentiated. The brain includes the following departments:
- front (telencephalon);
- intermediate (diencephalon);
- medium (mesencephalon);
- posterior (cerebellum).
The structure, degree of development, and function of each department in different classes of vertebrate subtype are significantly different.
Vertebral neurons form 2 types of substance:
- gray (consists of dendrites);
- white (formed by axons).
Axons are surrounded by an insulating sheath - a neurolemma that ensures the independence of the passage of pulses.
The spinal cord can be of various shapes (flat tape or rounded cord). It is located in the channel formed by the upper arches of the vertebrae. In the spinal cord there is a cavity - a neurocele, which is surrounded by gray matter (white is located outside).
The brain and spinal cord form the central nervous system, and the nerves that branch from them form the peripheral one. The system of nerve nodes concentrated near the spine forms an autonomous nervous system, which is divided into sympathetic and parasympathetic.
Skeleton and Musculature
Compared with the lower chordal skeleton, the representatives of the subtype of vertebrates are significantly differentiated and includes 3 main departments:
- skull;
- axial skeleton;
- belts and their limbs.
In cyclostomes and cartilaginous fish, the skeleton is completely constructed of cartilage. In other cranial regions, it consists of bones with a small proportion of cartilage.
Vertebrate subtype animals have 2 types of muscles:
- Somatic - is located under the skin and serves to carry out motor activity of the body, formed by striated muscle tissue. It develops from the dorsal mesoderm.
- Visceral - provides contractions of the internal organs (digestive tract, blood vessels, etc.), is represented by smooth muscles. It develops from the abdominal mesoderm.
The somatic muscles in the lower vertebrates are segmented (with the exception of the paired fins and jaw muscles), and in the higher ones it splits into separate groups that form different parts of the body (torso, head, locomotor organs, etc.).
Circulatory system
The circulatory system of the vertebrates is closed and is represented by three types of vessels:
- arteries (carry blood from the heart);
- veins (carry blood to the heart);
- capillaries (small vessels branching in the tissues).
The heart consists of striated muscle fibers, providing 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 arterial cone.
The circulatory system can be represented by one or two circles. The most effective system, in which 2 types of blood (arterial and venous) do not mix, are birds and mammals.
In the blood of vertebrates, there is a respiratory pigment hemoglobin, which carries oxygen, and shaped elements (red blood cells, lymphocytes, etc.).
Excretory system
The excretory organs of vertebrates are represented by paired kidneys, which remove excess fluid, salts and nitrogen metabolism products from the body. This organ has several varieties:
- pronephros (head kidney) - the most primitive type;
- mesonephros (trunk or primary kidney);
- metanephros (secondary or pelvic kidney).
From the blood to the kidney, the products pass through the Malpighian canals, and into the ureters through the Wolf.
Reproductive system
Reproductive organs, as a rule, are represented by paired ovaries or testes. Unlike skullless, vertebrates have genital ducts. In males, they are associated with the Wolf channel, and in females, with the Müller channel. The reproductive system of amniotes has a more complex structure than anamnias.