Abstract
The oral mucosa and the teeth of Lampetra japonica during metamorphosis were studied with scanning electron microscope to elucidate the details of the surface structure.In ammocoete larvae, the oral cirri located below the oral hood consist of many branches and are covered entirely by minute microvilli and a few ciliary bundles.In conjunction with the metamorphosis, the oral cirri differentiate into a small number of branched papillae and develop further into truncated ones.Simultaneously, the microvilli covering the oral mucosa transform into microridges in a labyrinthine pattern and finally into network-like microridges.Differentiation and eruption of horny teeth occur in the stage of the late macrophthalmia.The surface of the newly formed primary cornified layer is equipped with microridges and microrecesses as seen in that of the adult lamprey.Compared with those of other vertebrates possessing keratinized spines, the teeth of lamprey seem to be highly specialized in histological structure.
