The frond-like fimbriae surrounding the oral disc of the lamprey, Geotria australis, have been examined in living specimens, and by using histological, histochemical and ultra-structural techniques. Approximately 57 fimbriae are present in this species, with those at the posterior end of the disc being significantly larger than those in the anterior and lateral regions. The terminal finger-like projections of the fimbriae possess a stratified epithelium composed solely of a series of rows of mucous-producing cells. Tests have shown that the mucus of the epithelial cells contains large amounts of N-acetyl neuraminic acid. Since the adjacent fimbriae are closely apposed when the lamprey is using its oral disc for suction, it is suggested that their flexible shape, mucous secretions and production of an increased surface area for attachment, help to provide a more efficient seal. Since fimbriae are present in all lampreys except those species belonging to the Mordaciidae, it is postulated that their absence in this latter family can be related to known differences in the behaviour of their adult stages.