Satellite species among the holarctic lampreys (Petromyzonidae)

The new term 'satellite species' is used to replace the less accurate and by now obsolete term 'paired species.' Among lamprey genera a complex of species is usually found: one parasitic or 'stem' species and one or several nonparasitic or 'satellite' species probably derived from it. Among eight genera of holarctic lampreys the interrelation between the number of parasitic (p) and satellite (s) species is as follows: Caspiomyzon, 1p and no s; Petromyzon, 1p and no s; Ichthyomyzon, 3p and 3s; Tetrapleurodon, 1p and 1s; Entosphenus, 3p and 3s; Lampetra in Europe, 1p and 2s, in North America, 1p and 3s; Eudontomyzon in Europe, 1p and 3s, in Asia, 1p and no s; Lethenteron, 1p and 5s. Thus among the six polyspecific genera of the holarctic lampreys, 12 parasitic and 20 satellite species are presently known.