Section 2

Jawless and Cartilaginous Fishes

• Fishes have streamlined bodies, paired fins, and secrete mucus that reduces friction when swimming. The fish body plan makes them well suited to aquatic life.

• Fishes have a variety of organs that allow them to sense their environment. Fish can see, smell, and taste the world around them. They can also sense vibration, and some can sense electrical fields.

• Like early vertebrates, living agnathans lack jaws and paired fins and retain a notochord throughout life.

• Lampreys and hagfish are two types of jawless fishes that are alive today. Hagfishes burrow into and eat dead fish. Parasitic lampreys attach themselves to their host with their disc-shaped mouths and feed on the host's blood.

• Cartilaginous fishes have internal skeletons made of cartilage, and their skin is covered with placoid scales.

• Jawless fishes reproduce by external fertilization (fertilization occurs outside of the body of either parent). Most cartilaginous fishes reproduce by internal fertilization (the male inserts sperm into the female's body, and the young develop in an egg inside the female).

Vocabulary chemoreception (p. 783) external fertilization (p. 784) lateral line (p. 783) cartilage (p. 784)

placoid scale (p. 784) internal fertilization (p. 786)

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