Petromyzontidae, also known as Octopus and Qixingzi, is a family of the order lampreys of the subclass lampreya, and its suborder is one of the few remaining jawless vertebrate fish-like animals. The oldest lamprey fossil has a history of 360 million years, before dinosaurs appeared. Therefore, lamprey is called "living fossil", which plays an important role in studying the evolution of vertebrates.
The lamprey has a lateral oblate shape, and its tail shape is the original tail shape, with a body length of about 30cm；. The body is divided into three parts: trunk and tail. The skin is bare without scales.
Head: a single nostril is opened on the midline between the eyes on the top of the head, and the pineal eye is in the skin behind the nostril; The top eye is located below the pineal eye; There are 1 pairs of eyes without eyelids before the opening of branchial bursa on both sides of the head; Located on both sides of the head and behind the eyes, there are 7 circular gill slits (hence the name lamprey). In the past, some people thought that its branchial fissure was the eye, with seven branchial fissures and eight holes in the eye, so it also had another name.
On the ventral side of the front end of the body, there is a circular funnel-shaped mouth funnel with no mandible. There are yellow horny teeth on the inside of the mouth funnel and special "file teeth" with horny teeth on the tongue end.
Trunk: There are only odd fins, but no lateral fin. There are 1-2 dorsal fins on the dorsal midline. There are differences between male and female adult dorsal fins, and the male second dorsal fin is higher.
Tail: a caudal fin, which is symmetrical in appearance and internal skeleton, showing the original tail shape.
Relationship with human beings
An East Asian lamprey, which used to live in the ocean, became an invasive species after being accidentally brought into the Great Lakes of North America.
As the adult lamprey of East Asia lives on the blood of other fishes, their invasion has caused great losses to the fisheries of the Great Lakes, especially the Salvelinus namaycush and the Coregonus migratorius.
The European lamprey is also a kind of food, and the upper class in Europe has regarded it as a delicacy since the Middle Ages. According to the literature, Henry I, the king of England, loved to eat European lampreys, and once died after eating too many European lampreys in Normandy.
Until today, in some countries in southern Europe (France, Spain, Portugal, etc.), lamprey is still an expensive and famous dish. Due to overfishing, the population of lamprey in Europe has been decreasing.