The sea lamprey, Petromyzon marinus, is most likely to be seen in British rivers at this time of year as the adults swim upstream to spawn.
They are remarkable creatures but good looks are not one of their attributes. They resemble an eel and have a permanently open mouth with a great number of teeth. They also have some nasty parasitic habits.
Perhaps the most extraordinary thing about them is that they have been around since well before the dinosaurs, and with 360-million-year-old fossils looking remarkably like modern lampreys, they are said to be the oldest vertebrates.
Having thrived all that time they have suffered greatly in the UK from pollution and human interference with the flow of rivers, which has prevented them reaching their spawning grounds.
However, the cleaning up of the rivers and provision of passes to allow them to get round weirs and other obstructions has allowed them to recolonize rivers that had not seen a lamprey for many years, including the Great Ouse, Trent, Derwent and Wear.
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