Final answer:
Vertebrates, belonging to the phylum Chordata and subphylum Vertebrata/Craniata, are characterized by their vertebral column, well-developed brain, internal skeleton, and closed circulatory system, among other complex traits.
Step-by-step explanation:
Vertebrates are a diverse and complex group of animals within the kingdom Animalia and the phylum Chordata. These organisms are distinguished by a series of unique traits, with the vertebral column, or backbone, being the primary characteristic. The vertebral column made up of individual vertebrae and sometimes cushioned by intervertebral discs, provides structural support and protects the spinal cord.
In addition to the vertebral column, vertebrates possess a well-developed brain housed within a cranium, an internal skeleton composed of cartilage or bone, and a closed circulatory system with a multichamber heart that efficiently pumps oxygenated blood throughout the body.
Other defining traits of vertebrates include complex organ systems such as the excretory system with kidneys and an adaptive immune system. They also have a system of muscles attached to the endoskeleton that enables movement, working in an opposing pair's manner for efficient locomotion.
The subphylum Vertebrata/Craniata includes a diverse array of living species categorized into groups like Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia. These classes illustrate the wide range of anatomical and physiological adaptations that allow vertebrates to inhabit various environments on Earth.