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Anaspids were small marine agnathans that lacked heavy bony shield and paired fins, but have a striking highly hypocercal tail. They first appeared in the Early Silurian, and flourished until the Late Devonian extinction, [17] where most species, save for lampreys, became extinct due to the environmental upheaval during that time.
Agnatha (/ ˈ æ ɡ n ə θ ə, æ ɡ ˈ n eɪ θ ə /; [3] from Ancient Greek ἀ-(a-) 'without' and γνάθος (gnáthos) 'jaws') is a paraphyletic infraphylum [4] of non-gnathostome vertebrates, or jawless fish, in the phylum Chordata, subphylum Vertebrata, consisting of both living (cyclostomes) and extinct (conodonts, anaspids, and ostracoderms, among others).
Priscomyzon provides evidence that agnathans close to modern lampreys had existed before the end of the Devonian period.Lampreys have ancient origins, have endured for 360 million years and lived through four major extinction events - even so, their evolutionary history is obscure.
Anaspids were small, primarily marine agnathans that lacked heavy bony shield and paired fins, but have highly exaggerated hypocercal tails. They first appeared in the Early Silurian , and flourished until the Late Devonian extinction , [ 26 ] where most species, save for lampreys , became extinct.
Since then, opinions on the relations among jawless vertebrates have varied. Most workers have come to regard Agnatha as paraphyletic, having given rise to the jawed fishes. Because of shared features such as paired fins, the origins of the jawed vertebrates may lie close to Cephalaspidomorphi.
The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomina dubia), or were not formally published (nomina nuda), as well as junior synonyms of more established names, and genera that are no longer considered agnathans. Modern forms are excluded from this list.
The fish also has much longer lower pectoral-fin rays, the fins on the side of the body. The fins are “extended” and more full compared to other scorpionfish that live in the area, the ...
This last theory was based on the fact that they seem to have a paired olfactory organ and a sensory-line pattern which is quite similar to that of the gnathostomes. These characteristics are, however, likely to be general for either the vertebrates or, at any rate, for the ensemble of all ostracoderms and the gnathostomes.