agnatha defined in 1951 year

agnatha - agnatha;
agnatha - Class of vertebrates (sometimes made a sub-phylum, the other vertebrate classes then being grouped as the sub-phylum Gnathostomata). Represented now by very few species (order Cyclostomata, i.e. the lampreys and hagfishes). Aquatic, fish-like in many respects, but without jaws, and the two pairs of fins or legs characterizing nearly all other vertebrates are absent (though there may be one pair). The earliest fossil vertebrates known belong to this group; these are the Heterostraci, which lived in the Silurian (possibly Ordovician) 400 to 450 million years ago.

near agnatha in Knolik

letter "A"
start from "AG"

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