-Priyanti, Subject Matter Expert at Edumarz
Solution: The subphylum Vertebrata is mainly divided into two groups – Agnatha (jaws absent) and Gnathostomata (jaws present). The former includes jawless fishes such as lampreys and hagfishes, belonging to the class Cyclostomata. They are the first invertebrates and possess notochord throughout their lives. In contrast, the notochord in Gnathostomata is replaced by a vertebral column. This group is divided into two superclasses of Pisces and Tetrapoda. Pisces use gills for respiration and possess fins for locomotion. They include both cartilaginous and bony fishes Tetrapods are so named because of their locomotory organs – two pairs of pentadactyl limbs. They are further classified into classes Amphibia, Reptilia, Aves and Mammalia. The members of each of these classes possess a set of unique characteristics that sets them apart from the other classes.