Three arrangements of these lineages are possible, and two have been widely championed in recent years. 1), the precise relationship between the lamprey, hagfish and jawed vertebrate lineages has been more controversial. The latter are accordingly known as jawed vertebrates, or gnathostomes (see Glossary, Box 1), and several other characteristics support this separation, perhaps most notably the presence of paired fins/limbs and a mineralised skeleton in the gnathostomes and their absence in cyclostomes.Īlthough there is general consensus that living gnathostomes comprise a clade ( Fig. Together, lampreys and hagfish are usually referred to as the cyclostomes, ‘agnathans’ or jawless vertebrates (see Glossary, Box 1), and, as these names imply, they lack the hinged jaws characteristic of other living vertebrates. They lack clear vertebrae allowing them to tie their body in a knot, and they can produce huge quantities of slime when provoked. Hagfish, by contrast, are typically deep-sea scavengers, feeding on sunken carcasses by burrowing inside via an orifice or wound. Rasping, tooth-like structures then grind into host flesh for feeding. Most lampreys are ectoparasites on fish, using a circular, sucker-like mouth to clamp onto their hosts. Lampreys and hagfish are unusual animals, and you are not likely to forget them if you have seen them.
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