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The first fish evolved as many as 700 million years ago. They were jellyfish. These creatures didn't have brains, mouths, or spines. Then, some 500 million years ago, jawless fish were formed. These included lampreys and hagfishes that had backbones and brains but did not have jaws.
These fish didn't look like the fish we know today; they looked more like snakes. They had long slithery bodies. Some even had dorsal fins. They typically had eyes similarly placed on their bodies as snakes' eyes are, with gills and no scales. While these fish don't have jaws, that doesn't mean they can't eat. They have sharp teeth in their mouths. They attach their teeth to their prey and slowly eat their food. They rock their teeth back and forth and eat the creature's blood and flesh. These fish eventually evolved to more of today's common fish with jaws and wider bodies.
Some types of these fish still exist in some of the warmer waters across the globe. Some forms of lampreys and hagfish resemble some amphibians and have larval stages, during which time they feed on algae and other sea life. The larval phase typically lasts as long as three years, and the transformation takes about four or five months. They can grow up to two pounds in weight and can be as long as three feet. Adult jawless fish will eat other fish and creatures.
When these fish spawn, they find a shallow area where they clear away with their suction-like mouths and build a nest. Some hagfish, however, are believed to prefer deep waters in which to breed. The eggs of these creatures are usually fairly large and are formed in a tough outer casing. The male and females attach themselves to a rock in the water. The male wraps his body around her, and the pressure he creates helps release the eggs.