Chordata Subphyla Vertebrata Classes The Subphylum Vertebrata can be further categorized into classes. Vertebrates have a skull and a spine. The parts of the skeleton that form the spine are called vertebrae. The skeleton can be made of bone or cartilage. Placodermi (Armored Fish) About Dunkleosteus The now extinct placoderms had strong armor covering their head. Agnatha (Jawless Fish) Coming Soon They have a cartiliginous skeleton (a skeleton made of cartilage). Chondricthyes (Cartilaginous Fish) Coming Soon They have a cartiliginous skeleton. Osteichthyes (Bony Fish) Coming Soon They have a bony skeleton (a skeleton made of bones). Amphibia (Amphibians) Coming Soon They have a bony skeleton. Reptilia (Reptiles) Coming Soon They have a bony skeleton. Aves (Birds) Coming Soon They have a bony skeleton. Mammalia (Mammals) Coming Soon They have a bony skeleton.