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Animals

What are lampreys and borers modern primitive fish

The lampreys and borers are the most primitive of living animals with backbones. Eel-shaped, jawless, scaleless fish with a single nostril, they lack the paired fins we find in most other fishes. For feeding, they possess a rough, rasping tongue, with which they scrape away an entrance to the body cavities of other fishes.

In all, we are acquainted with about fifty species of these creatures (class Cyclostomi, a word meaning “circular mouths”). They range from six inches to about three feet in adult size.

All of the borers, which include the hagfishes and slime-eels, are ocean dwellers, and lay relatively large eggs with a protective, horny shell. Unlike the lampreys, they seldom, if ever, are able to attack living prey, but eat their way inside fishes that are injured, or trapped in gill nets (nets that catch on the gill covers when the fish tries to back out). The borers devour their victims completely, except for head, skin, and the larger bones.

The Sea Lamprey, Petromyzon marinus, is a repulsive-looking fish with a mode of life that befits its appearance. It has a long, eel- like body, covered with scaleless skin that grades from whitish on the belly to grayish blue on the back in young adults, older individuals becoming mottled. Its only fins are a small caudal (tail) fin and two small dorsal (back) fins. It has a pair of well-formed eyes, and behind each of these stretches a series of seven holes which lead into the gills. A single nostril opens midway between the eyes.

Instead of jaws, the lamprey has a round, sucking mouth, lined with more than a hundred sharp teeth and containing a pistonlike tongue also armed with teeth. With its sucking mouth the lamprey fastens itself onto a fish, then rasps a hole in it, and sucks out its blood and body fluids. Lampreys sometimes attach themselves to large sharks and to boats and are capable of overtaking and fastening onto motorboats traveling fifteen miles per hour. Occasionally they attach themselves to human swimmers, but do not feed on them, although they have been known to cut out lumps of tissue from whales to which they have fastened themselves.

There are about twenty-five different kinds of lampreys, and they are found in both fresh and salt waters of many parts of the world. Those that live in the ocean, like the sea lamprey, go into fresh water to spawn. In the spring full-grown sea lampreys, ranging from about two to three feet in length, enter streams on our Atlantic coast. They sometimes employ their sucker-mouths to ascend waterfalls and rapids, and always use them to build their nests. Both male and female cooperate in moving stones to form a depression in which the small eggs, sometimes more than 200,000 are laid. After one spawning, lampreys die. The young larvae do not resemble their parents at all and are called ammocoetes. For at least three years they burrow in the mud, feeding on small bits of organic matter that they sift out of the ooze. Finally they change into the adult form and go back to the sea.