Agnatha, the superclass of jawless fish in the phylum Chordata, includes both present (cyclostomes) and extinct species. Cyclostomes, such as lampreys and hagfishes, lack jaws and have unique adaptations. They have primitive characteristics like a circular mouth and lack of paired fins, alongside sp

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Lymphoid organs play a crucial role in the defense mechanisms of finfish and shellfish by generating immune cells. Different types of fish vary in their lymphoid organ structures, with jawless fish relying on lymphoid tissue within other organs for immune cell production. Cyclostomes, like hagfish a

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