The urogenital papilla in the Holarctic lamprey (Petromyzontidae)

The urogenital papillae of 30 species of Holarctic lampreys were examined to determine if this structure has any taxonomic use. Total length, branchial length and papilla length were measured. A correlation between mean papilla length and mean total length of the species existed in males for parasitic species but not nonparasitic species, indicating a potential use in nonparasitic species. In nonparasitic species the most obvious differences existed in the papilla length: branchial length ratio. From the limited material available there appeared to be no geographic variation in this ratio, although there is a seasonal variation with the ratio increasing as spawning approaches. It therefore appears that urogenital papilla length has taxonomic value in male nonparasitic lampreys, provided the specimens are collected in spawning condition. The female papilla is too small to be of use.