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The earliest lamprey with the specialised toothed oral disc typical of modern lampreys is Yanliaomyzon from the Middle Jurassic of China around 163 million years old, which is thought to have had a predatory lifestyle like modern lampreys, and probably had a three stage life cycle including ammocoetes. [6]
If lampreys are included, they would extend the known range of the group from the Silurian and Devonian periods to the present day. They are the closest relatives of jawed fishes , who may have emerged from within them; if this is true, they would survive if the jawed fish are included.
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).
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]
Like other lampreys, it has no jaws, only a sucker. The skin is a striking silver in adult lampreys caught fresh from the sea but soon changes to brown after they have been in fresh water for some time, due to deposition of biliverdin. [9] Adult's eyes are relatively small and located on the side of the head.
The Caspian lamprey is a slim-bodied, eel-like fish that grows to a length of about 40 cm (16 in). The longest recorded specimen was 55 cm (22 in) long and weighed 206 g (7.3 oz). Like other lampreys, it has no jaws, but it has a round oral disc surrounding the mouth. Inside this it has several radiating rows of tiny, backward-facing teeth.
Lampetra ayresii is a species of lamprey in the family Petromyzontidae.It is also called the river lamprey or western river lamprey.It is found in the eastern Pacific, specifically from Tee Harbor, Juneau in Alaska to the Sacramento–San Joaquin drainage in California, USA.
In larval lampreys, called ammocoetes, their mouth is not fully developed, very small, and hidden between folds of skin. Adults have a disk shaped mouth with varying amounts of teeth depending on the species. The Ohio lamprey has a single, continuous dorsal fin. Fully grown, Ohio lampreys reach 10–14 inches, but may get to 15 inches.