Lampreys: Common name for the only family (Petromyzontidae) of eellike fish in the order Petromyzontiformes. They are jawless but have a sucking mouth with horny teeth.Petromyzon: A genus of primitive fish in the family Petromyzontidae. The sole species is Petromyzon marinus, known as the sea lamprey. The adult form feeds parasitically on other fish species.Hagfishes: Common name for a family of eel-shaped jawless fishes (Myxinidae), the only family in the order MYXINIFORMES. They are not true vertebrates.Physiology, Comparative: The biological science concerned with similarities or differences in the life-supporting functions and processes of different species.Fishes: A group of cold-blooded, aquatic vertebrates having gills, fins, a cartilaginous or bony endoskeleton, and elongated bodies covered with scales.Swimming: An activity in which the body is propelled through water by specific movement of the arms and/or the legs. Swimming as propulsion through water by the movement of limbs, tail, or fins of animals is often studied as a form of PHYSICAL EXERTION or endurance.Spinal Cord: A cylindrical column of tissue that lies within the vertebral canal. It is composed of WHITE MATTER and GRAY MATTER.Vertebrates: Animals having a vertebral column, members of the phylum Chordata, subphylum Craniata comprising mammals, birds, reptiles, amphibians, and fishes.Reticular Formation: A region extending from the PONS & MEDULLA OBLONGATA through the MESENCEPHALON, characterized by a diversity of neurons of various sizes and shapes, arranged in different aggregations and enmeshed in a complicated fiber network.Pyrrolidonecarboxylic Acid: A cyclized derivative of L-GLUTAMIC ACID. Elevated blood levels may be associated with problems of GLUTAMINE or GLUTATHIONE metabolism.Locomotion: Movement or the ability to move from one place or another. It can refer to humans, vertebrate or invertebrate animals, and microorganisms.Chordata, Nonvertebrate: A portion of the animal phylum Chordata comprised of the subphyla CEPHALOCHORDATA; UROCHORDATA, and HYPEROTRETI, but not including the Vertebrata (VERTEBRATES). It includes nonvertebrate animals having a NOTOCHORD during some developmental stage.