Vertebrata (Vertebrata) Vertebrata (Chordata) is the general name of vertebrate subfamily. The largest number, the most complex structure and the highest evolutionary status. The morphological structure is very different from each other, and the lifestyle is very different. In addition to the * * * characteristics of chordates, other features include: ① the head appears obviously, the central nervous system is tubular, the front end expands into the brain, and the spinal cord differentiates behind it. ② Most kinds of notochord are only seen in the early stage of development (except for Cirrhonchus, Chondrichthyes and teleost), and then they are replaced by the spine connected by a single vertebra. (3) Primary aquatic animals breathe through gills, while secondary aquatic animals and terrestrial animals only have branchial cleft in embryonic stage, while adults breathe through lungs. (4) Except for Cirrhostoma, they all have upper and lower jaws. ⑤ The circulatory system is relatively perfect, and a contractile heart appears, which promotes blood circulation and is conducive to improving physiological functions. ⑥ Replacing the simple renal tube with a kidney with complex structure can improve the excretory function, and a large amount of waste produced by metabolism can be excreted more effectively. ⑦ Except for Cirrhostoma, aquatic animals have lateral fin, and terrestrial animals have paired appendages. This subfamily includes: Circadian, Chondrichthyes, teleost, Amphibia, Reptilia, Birds and Mammalia. Although there are significant differences in the characteristics of each class, the organ systems that make up the body and their functions are basically the same. Squid, right