They consist of two distinct series: the series of bony fish, in other words, those whose spines have vertebrae made of bone; and cartilaginous fish, in other words, those whose spines have vertebrae made of cartilage.
Componen dos series distintas: la de los peces óseos, es decir, la de aquellos cuya espina dorsal está constituida por vértebras óseas, y la de los peces cartilaginosos, cuya espina dorsal está hecha de vértebras cartilaginosas.