AP BIOLOGY

Detailed explanation-1: -Agnatha (/ˈæɡnəə, æɡˈneɪə/, Ancient Greek - ‘without jaws’) is an infraphylum of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species.

Detailed explanation-2: -Evolution. If evidence from fossil and living forms is combined, the Agnatha are distinguishable from the other craniates (Gnathostomata) by what they lack: jaws, lateral fins supported by fin rays, vertebrae, a horizontal semicircular canal in the ear, and genital ducts.

Detailed explanation-3: -Cyclostomes: Hagfish and Lampreys In fact, they are the only two groups of extant vertebrates that lack jaws.

Detailed explanation-4: -Agnatha (’without jaws’) is a jawless fish superclass in the phylum Chordata, subphylum Vertebrata, that includes both living (cyclostomes) and extinct (conodonts and ostracoderms) species. The group is related to all vertebrates with jaws, which are referred to as gnathostomes.

Detailed explanation-5: -Aganthans do not have hinged upper and lower jaws, instead they have unhinged circular mouths. They also do not have paired appendages like other vertebrates but have a tail and a caudal fin. The internal skeleton is made from cartilage and their body covering is skin.