cyclostome (sĪˈkləstōmˌ) [key], jawless fish, member of the Cyclostomata, the only living order of the vertebrate class Agnatha (see Chordata). This group includes the hagfish and the lamprey. The name also applies to members of the order Cyclostomata of the invertebrate phylum Ectoprocta, class Gymnolaemata.

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