(phylum Chordata, subphylum Vertebrata)
Superclass of jawless, fish-like vertebrates, with sucker-like mouths, including the extant lampreys, slime-eels and hagfish, and some of the earliest primitive vertebrates, with heavily armoured forms, e.g. Cephalaspis (see also osteostraci), Pteraspis (see heterostraci), and Jamoytius (see anaspida). They appeared first during the Ordovician.
Subjects: Zoology and Animal Sciences — Earth Sciences and Geography.