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Hagfish, which resemble lampreys, have traditionally been considered the sister taxon of the true vertebrates (lampreys and gnathostomes) [36] but DNA evidence suggests that they are in fact the sister taxon of lampreys. [37] The heart of the lamprey is anterior to the intestines.
Lampetra is a genus of lampreys in the family Petromyzontidae.. Phylogenetic studies indicate that this genus as presently defined is polyphyletic, with species of this genus from western North America forming a clade that forms the sister group to Lethenteron, Eudontomyzon, and Lampetra sensu stricto (eastern North American and European species).
For a fuller treatment of this taxonomy, see the vertebrate article. The position of hagfish in the phylum Chordata is not settled. Phylogenetic research in 1998 and 1999 supported the idea that the hagfish and the lampreys form a natural group, the Cyclostomata, that is a sister group of the Gnathostomata. [3] [4]
Petromyzontidae are a family of lampreys native to the Northern Hemisphere, comprising the vast majority of living lampreys. [1] Petromyzontids have the highest number of chromosomes (164–174) among vertebrates.
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]
The term sister group is used in phylogenetic analysis, however, only groups identified in the analysis are labeled as "sister groups".. An example is birds, whose commonly cited living sister group is the crocodiles, but that is true only when discussing extant organisms; [3] [4] when other, extinct groups are considered, the relationship between birds and crocodiles appears distant.
The Pacific lamprey (Entosphenus tridentatus) is an anadromous parasitic lamprey from the Pacific Coast of North America and Asia in an area called the Pacific Rim. [4] It is a member of the Petromyzontidae family. The Pacific lamprey is also known as the three-tooth lamprey and tridentate lamprey. Ammocoetes held by biologist in the Carmel River
The silver lamprey is an eel-like fish with an attenuate body composed of 49–52 clearly defined segments (i.e. myomeres, between the last gill slit and the anus).Silver lampreys possess a cartilaginous skeleton, and adults generally grow to a length of 12 inches and are silvery or bluish in color when spawning.