Lampreys and Hagfishes

Hagfishes are entirely marine animals, living in burrows dug into the sediment of the sea floor of the temperate waters of the continental shelves. They have degenerate, non-functional eyes, and appear to rely mostly on short, sensory tentacles around their mouth for detecting their food. Hagfishes have a single nostril, through which water is taken in and used to ventilate the gas-exchange surfaces of their gill pouches before being discharged back to the ambient environment through gill slits. Hagfishes have four distinct blood-pumping regions in their circulatory system, which represent four functional hearts.

Group of Pacific lampreys. Photograph by Gary Gibson. Photo Researchers, Inc. Reproduced by permission.

A single, elongated gonad on the front part of hagfishes develops into an ovary in females, and the back part into a testis in males. In 1864, the Copenhagen Academy of Sciences offered a prize for the first zoologist to describe the method by which hagfish eggs get fertilized. This prize has yet to be claimed! Hagfish feed largely on invertebrates, especially polychaete worms. They also feed on dead fish, which they enter through the mouth, and then eat from the inside out. Hatchlings of hagfishes resemble the adults, and therefore are not, strictly speaking, larvae.

Hagfishes are extremely slimy creatures. Their mucous may protect them from some types of predators, but it can also represent a problem to the hagfish, by potentially plugging its nostril. Hagfishes periodically de-slime themselves by literally tying themselves into a tight knot, which is skillfully slid along the body, pushing a slime-ball ahead of itself. This unusual, knotty behavior is also used by hagfishes to escape from predators, and to tear into the flesh of dead fish.