Agnathans (meaning ‘without jaws’ Ancient Greek), are a paraphyletic infraphylum of animals characterised by a lack of jaws. Consisting of both living and extinct clades, the oldest fossils of them appeared in the Cambrian. Currently, there are about 120 species of jawless fishes, including hagfish and lampreys.
<- lamprey
They are ectothermic. Due to their metabolism slowing in cold waters, they do not have to eat very much. Without a distinct stomach, agnathans instead have a long gut, which is pretty much homogenous throughout its length.
Along with not having jaws, agnathans are further characterised by: Their lack of paired fins, the presence of a notochord, and seven or more gill pouches. They reproduce externally and aren’t caring parents tbh.