Permanently-attached males have only been observed in 5 of the 11 ceratioid families (10 out of 35 genera, 23 out of 160 known species). All other ceratioid groups undergo somewhat similar behaviors, but the males are either facultative parasites or only attach temporarily during mating. In more distantly-related groups of anglerfish, the males never attach to the females, making the parasitic or semi-parasitic reproductive relationship unique to ceratioids (Vollrath 1998, Pietsch 2005).