Placodermi - extinct
Chondrichthyes (cartilaginous fish)
Acanthodii - extinct
Actinopterygii (ray-finned fish)
Vertebrata is a subgroup of chordates, specifically, those with backbones or spinal columns. Vertebrates are definied as chordates whose notocord is protected by bones called vertebrae. It is the largest and most advanced subphylum, and contains most of the animals with which we are familiar. Fish (including lampreys but excluding hagfishes), amphibians, reptiles, birds, and mammals (including humans) are vertebrates.