The morphology of the olfactory epithelium in larval, juvenile and upstream migrant stages of the sea lamprey, Petromyzon marinus.

The structure of the olfactory epithelium in the larval, juvenile and upstream migrant stages of the sea lamprey, Petromyzon marinus, was investigated by light microscopy and by scanning and transmission electron microscopy. Ciliated olfactory receptor cells (ORC) were present in all stages. In larval specimens, the number of ORC was 20 +/- 8 ORC per 100 microns length of olfactory epithelial surface. In juveniles and in upstream migrants the ORC density dropped to 9 +/- 2 and 6 +/- 2 ORC/100 microns, respectively. Sustentacular cells were microvillar in the smallest larval stage (with a body length of 15 mm) and ciliated in larger larvae and later life stages. The morphological characteristics of the olfactory mucosa suggest that the sea lamprey's capacity for use of the olfactory system extends into the larval stage, and that there are specific changes associated with metamorphosis.