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These two groups are easily distinguished, one from the other, by the fact that the hags have several barbels on the chin, that their mouths are not disc- or funnel-like, that they have only one continuous fin fold on the back and around the tail, and that their eyes are not visible externally, whereas the lampreys have no barbels, their mouths are disc- or funnel-like, their eyes are well developed after the larval stage is past, and they have one or more dorsal fins separate from the caudal fin.