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Agnatha (/ ˈ æ ɡ n ə θ ə, æ ɡ ˈ n eɪ θ ə /; [3] from Ancient Greek ἀ-(a-) 'without' and γνάθος (gnáthos) 'jaws') is a paraphyletic infraphylum [4] of non-gnathostome vertebrates, or jawless fish, in the phylum Chordata, subphylum Vertebrata, consisting of both living (cyclostomes) and extinct (conodonts, anaspids, and ostracoderms, among others).
Gnathostomata is traditionally a infraphylum, broken into three top-level groupings: Chondrichthyes, or the cartilaginous fish; Placodermi, an extinct grade of armored fish; and Teleostomi, which includes the familiar classes of bony fish, birds, mammals, reptiles, and amphibians. Some classification systems have used the term Amphirhina.
Cyclostomi, often referred to as Cyclostomata / s ɪ k l oʊ ˈ s t ɒ m ə t ə /, is a group of vertebrates that comprises the living jawless fishes: the lampreys and hagfishes.Both groups have jawless mouths with horny epidermal structures that function as teeth called ceratodontes, and branchial arches that are internally positioned instead of external as in the related jawed fishes. [1]
Jawless fish belong to the superclass Agnatha in the phylum Chordata, subphylum Vertebrata. Agnatha means 'un-jawed, without jaws' (from Ancient Greek). [11] It excludes all vertebrates with jaws, known as gnathostomes. Although a minor element of modern marine fauna, jawless fish were prominent among the early fish in the early Paleozoic.
Other elements of the skull, however, may be reduced; there is little cheek region behind the enlarged orbits, and little, if any bone in between them. The upper jaw is often formed largely from the premaxilla , with the maxilla itself located further back, and an additional bone, the symplectic, linking the jaw to the rest of the cranium.
On July 14, 2022, YouTube made a special playlist and video celebrating the 317 music videos to have hit 1 billion views and joined the "Billion Views Club". [65] [66] On April 1, 2024, the communications app Discord incorporated a short trailer video into their in-app April Fools' Day prank regarding loot boxes. The video automatically looped ...
YouTube Music is a music streaming service developed by the American video platform YouTube, a subsidiary of Google. The service is designed with a user interface that allows users to explore songs and music videos on YouTube -based genres, playlists, and recommendations.
The name Craniata usually appears when hagfishes are thought to be outside the clade comprising lampreys and gnathostomes (which is then called Vertebrata). In that case, Agnatha usually includes hagfishes anyway, because it's then defined as non-gnathostome craniates. Lampreys and hagfishes are pretty much the canonical extant agnathans.