Vertebrata

(′vərd·ə′bräd·ə)

(vertebrate zoology) The major subphylum of the phylum Chordata including all animals with backbones, from fish to human.

---

The major subphylum of the phylum Chordata, comprising the backboned animals, including humans. The subphylum is sometimes called the Craniata, because of the common possession of a cranium or braincase, but that term has dropped out of use in scientific nomenclature.

The characteristic features of the Vertebrata are a vertebral column, or backbone, and a cranium, which protects the central nervous system (brain and spinal cord) and major sense organs; the presence of bone, which is a tissue unique to vertebrates; and a neural crest of nerve cells that remain after the formation of the central nervous system. Other distinctive vertebrate features are a kidney, with the nephron as its functional unit; a heart; red and white blood cells; a liver and a pancreas; specialized sense organs, such as a complex eye, a lateral-line system, ears, and a sense of smell; several unique endocrine organs, such as the pituitary and thyroid; and a complex skin comprising an epidermis and dermis. See also Chordata; Vertebra.

Vertebrates evolved from a lower chordate similar to the present-day Cephalochordata (amphioxus). They originated in fresh water and developed a kidney as their organ of water balance. They became free-swimming, with several evolutionary lines invading the oceans. The main line of evolution in the vertebrates, that which led to the tetrapods, remained in fresh waters.

The Vertebrata are divided into the following eight classes, which are arranged into several partly overlapping informal groups, and often two superclasses, Pisces and Tetrapoda, are used to differentiate the aquatic and the terrestrial vertebrates.

     Superclass Pisces

           Class: Agnatha

                          Placodermi

                          Chondrichthyes

                          Osteichthyes

     Superclass Tetrapoda

          Class: Amphibia

                          Reptilia

                          Aves

                          Mammalia

Pisces (zoology)

The term Gnathostomata designates the seven classes of jawed vertebrates, in contrast to the jawless Agnatha. The Anamniota include the Pisces (fishes) and the Amphibia (amphibians). The Amniota consists of the Reptilia, Aves, and Mammalia. See also Amniota; Animal kingdom.

---

A subphylum of the Chordata, comprising all animals having a vertebral column, including mammals, birds, reptiles, amphibians and fish.

IN BRIEF: n. - Fishes; amphibians; reptiles; birds; mammals.