Jawless

Jawless fish are a type of fish that lack jaws. They are part of the superclass Agnatha, which includes both extinct and extant species. The two extant groups of jawless fish are the lampreys and the hagfish.

Characteristics

Jawless fish are characterized by their lack of a jaw, which is replaced by a circular, toothed, sucking mouth. They also lack paired fins and scales, and have a cartilaginous, notochord-supported skeleton.

Evolution

The first jawless fish evolved in the Cambrian period, over 500 million years ago. They were the first vertebrates, and their descendants include all other vertebrates. The evolution of jaws in fish is considered a key innovation that led to the success of the vertebrates.

Extant Groups

Lampreys

Lampreys are a type of jawless fish that are characterized by their eel-like bodies and toothed, sucking mouth. They are parasitic, attaching to other fish to feed on their blood and body fluids.

Hagfish

Hagfish are another type of jawless fish. They are known for their ability to produce large amounts of slime when threatened. Hagfish feed on dead and dying fish, burrowing into their bodies and consuming them from the inside out.

Extinct Groups

Many groups of jawless fish are now extinct, including the ostracoderms, which were heavily armored fish that lived from the Ordovician to the Devonian periods.

See Also

• Fish anatomy
• Evolution of fish
• Vertebrate

Jawless Resources
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