The Development of Teeth and Associated Feeding Structures During the Metamorphosis of the Lamprey, Geotria australis

The pattern of development of the teeth, laminae, piston, muscles, cartilages and fimbriae associated with the suctorial disc of lampreys has been investigated histologically during the seven stages of metamorphosis in the Southern Hemisphere species, Geotria australis . The cirrhi‐bearing hood of ammocoetes and the earliest stage of metamorphosis (S1) were indistinguishable. In stages S2, S3, S4, these cirrhi regressed and the supraoral lamina, piston and infraoral lamina primordial regions began to differentiate. The fifth stage (S5) was characterised by an elaboration of the annular cartilage and disc musculature, deposition of the tectal cartilage, initiation of tooth development, formation of oral fimbriae, and eruption of the keratin cone of the transverse lingual lamina. Subsequently (S6), the keratin cusps of the supraoral and infraoral laminae became exposed at the surface, and distinct retractor and protractor muscles formed around the lingual cartilage. In the latter part of the terminal stage in metamorphosis (S7), just prior to the time when the animal migrates downstream, the primary tooth cones and the keratin cusp of the longitudinal lingual laminae began breaking through the epithelial surface of the disc.