Gnathostomata

Gnathostomata is the vertebrate clade defined by jaws, encompassing cartilaginous fishes, bony fishes, tetrapods, and extinct relatives. Its members share paired appendages and several other derived traits.

Vertebrate: An animal with a backbone or a precursor structure called a notochord. Gnathostomata is a major clade within vertebrates.
Mandibular arch: The embryonic pharyngeal arch that forms much of the upper and lower jaws in vertebrates. Jawed vertebrate jaws develop from this ancestral skeletal arch.
Agnatha: A traditional grouping of jawless vertebrates, including living lampreys and hagfishes and many extinct forms. Jawless vertebrates provide the contrast for identifying the origin of gnathostome jaws.
Sharks: Cartilaginous fishes in the group Selachimorpha, with streamlined bodies and multiple gill slits. Sharks exemplify active predatory forms among living jawed vertebrates.
Jaw: A hinged skeletal structure that supports biting and food processing. Jaws are the defining feature from which the clade takes its name.
Pharyngeal arches: Repeated embryonic structures in the throat region that develop into parts of the face, jaws, and neck. Modification of the front arches supplied the structural basis for jaws.
Entelognathus: An extinct armored fish from the Silurian Period known from fossils preserving jaw bones resembling those of bony vertebrates. Its anatomy helps illuminate the early evolution of jawed-vertebrate jaws.
Batoidea: The cartilaginous-fish group comprising rays, skates, and guitarfishes. Batoids show how the cartilaginous-fish body plan diversified into flattened forms.
Paired fins: Fins occurring as left-right pairs, including pectoral and pelvic fins. Paired appendages are a key feature of jawed vertebrates and precede tetrapod limbs.
Hox genes: A family of developmental genes that helps establish body-region identities along the head-to-tail axis. Hox gene expression helps pattern the pharyngeal arches that form jaw structures.

Linked from 6 pages