Agnatha - Research Article from Macmillan Science Library: Animal Sciences

This encyclopedia article consists of approximately 2 pages of information about Agnatha.
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The group Agnatha consists of the jawless fishes, the most primitive group of extant vertebrates. While most agnathan species are now extinct, fossil evidence indicates that the group was once highly successful and extremely varied. Two lineages of agnathans have survived to the present, the lampreys and the hagfish.

Characteristics of Agnathans

As the most primitive members of the vertebrates, agnathans differ from all others in several important respects. First, they lack hinged upper and lower jaws and instead have unhinged circular mouths. They also lack the paired appendages (fins or limbs) that are found in other vertebrates. In addition, the internal skeleton of agnathans is not bony but cartilaginous. However, many extinct agnathans had extensively developed bony plates directly under the skin. These were most often found in the region of the skull and served as a protective armor. Bony plates are not present in extant agnathan...

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This section contains 536 words
(approx. 2 pages at 300 words per page)
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Agnatha from Macmillan. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.