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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).
Myllokunmingiidae is a group of very early, jawless prehistoric fish which lived during the Cambrian period. [2] The Myllokunmingiids are the earliest known group of craniates . The group contains only three known genera, Haikouichthys , Myllokunmingia , and Zhongjianichthys .
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]
A newfound fossil of a jawless fish is the oldest known vertebrate cranium preserved in 3D. The 455 million-year-old find could illuminate how vertebrate heads evolved.
After the appearance of jawed fish (placoderms, acanthodians, sharks, etc.) about 420 million years ago, most ostracoderm species underwent a decline, and the last ostracoderms became extinct at the end of the Devonian period. More recent research indicates that fish with jaws had far less to do with the extinction of the ostracoderms than ...
"A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Archived from the original on 2011-07-23; Sepkoski, Jack (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Archived from the original on 2011-07-23
Haikouichthys / ˌ h aɪ k u ˈ ɪ k θ ɪ s / is an extinct genus of craniate (animals with notochords and distinct heads) that lived 518 million years ago, during the Cambrian explosion of multicellular life. The type species, Haikouichthys ercaicunensis, was first described in 1999. [2]
A related species, the Gulf hagfish (Eptatretus springeri), occurs in the Gulf of Mexico. [7]To distinguish these two types of hagfishes, we can look at their lateral line and eyes, the Myxine glutinosa has no lateral line system and also an unpigmented, cornea-like window in the skin overlying the eye.