Lampetra richardsoni

Western Brook Lamprey (Lampetra richardsoni): Many lamprey species have a prolonged larval period, after which they metamorphose into a parasitic adult phase that attaches to and feeds on various fish species. The Western brook lamprey is a freshwater resident species that has evolved to forgo the parasitic lifestyle and instead spawn shortly after metamorphosis. Most species that have lost a parasitic stage have close relatives (or “paired species”) that are parasitic. In the case of the Western brook lamprey, this is the Western river lamprey (Lampetra ayresii). Thus far the Western brook lamprey is the only nonparasitic species that has been sequenced.
Like other lamprey species, the Western brook lamprey genome provides important comparative perspective on the evolution and maintenance of functions within other lamprey species and vertebrates in general.
Image from Wikipedia