Animal Sciences. A-Crep - download pdf or read online

By Allan B. Cobb

ISBN-10: 0028655575

ISBN-13: 9780028655574

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Evidence from the fossil record suggests that agnathans reached their peak of diversity between about 500 million and 340 million years ago. During this period, they were plentiful both in the seas and in freshwater habitats. More than 200 fossil species are known. The majority of these species were fairly small, perhaps a few inches long. The species that have survived to the present are but the remains of a group that was once considerably more diverse. S E E A L S O Phylogenetic Relationships of Major Groups.

The larva is of particular interest to biologists who study vertebrate evolution because it shares many features with the cephalochordate Branchiostoma (formerly called Amphioxus), which is the group believed to be most closely related to the vertebrates. The resemblance between Branchiostoma and the larval form of a very primitive vertebrate is striking, and supports the closeness of the relationship between the two groups. The second group of living agnathans is the hagfish. Hagfish are scavenger species that feed off dead and wounded organisms in the ocean.

An antibody is able to recognize and bind to a particular offending antigen. ” Invaders such as bacteria, viruses, fungi, toxins, and other foreign substances generally carry a variety of antigens on their surfaces. The antibody for a particular antigen functions by binding to that antigen. This results in one of two possibilities. The antibody may deactivate the antigen by either blocking its active site or otherwise changing it so that it can no longer harm host cells. Alternatively, an antibody may label the antigen-carrying object for destruction.

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Animal Sciences. A-Crep by Allan B. Cobb


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Categories: Zoology