chord type has more than 40 thousand. Living species.This includes bescherepnyh (tunicates and Amphioxus) and cranial (cyclostomes (lamprey), fish, amphibians, reptiles, birds and mammals).Representatives of this type are found around the globe and in all habitats.Most chordates lead an active, mobile lifestyle, but there are species that are attached to the substrate - tunicates.Dimensions and weight vary greatly from this type, depending on the species and habitats.
Despite the fact that the animals in the combined type of chord, very different in appearance, peculiarities of the internal structure, way of life and the environment, they have a number of common features.To determine this similarity will help general characteristic of chordates.
all chordates have:
-
axial skeleton, which is represented by a chord at bescherepnyh have cranial and spine.The skeleton has a shape strand performs a supporting function and gives elasticity body.
-
Gill slits in the throat.In protostomes organisms that live all the time in the water and do not leave her, gill slits remain throughout life.And deuterostome who left the water environment, and then go back (dolphins, whales, crocodiles), and land animals gill slits exist only at certain stages of embryonic development, and then disappear.Instead functioning lungs - breathing terrestrial bodies.
-
central nervous system (CNS), which is in the form of a tube located on the side of the back.In primitive chordate it in the form of a hollow tube remains throughout life, and in higher animals is divided into the brain and spinal cord.And the nerves that extend from the central nervous system, form the peripheral nervous system.
-
blood closed system.The heart, like the neural tube, is located on the ventral side of the body.
chordates have distinctive traits within a species, because of their way of life and habitat, as well as adapting to it.In addition to the signs of the differences from other organisms, in chordates and have similarities with other animals.These similarities:
-
Bilateral symmetry that is inherent in flat worms, insects and other organisms.
-
Overall (aka secondary body cavity), which contains the internal organs.Secondary cavity appears in annelids.
-
have secondary mouth, which is formed in the gastrula stage by breaking the wall.
-
metamerically layout of the (segment), clearly expressed at the stage of the embryo and in primitive chordates, in adult animals can be seen in the structure of the muscles and the vertebral column.In this type of chord detect signs of resemblance to annelids and insects.
-
presence of organ systems - circulatory, respiratory, nervous, digestive, excretory, reproductive.
Thus, the type of chord combines animals, which have a bilateral symmetry and overall, the presence of gill slits in the early stages of development and the emergence of the internal skeleton - chords, over which is the neural tube.Under the chord is a digestive tube.
