Lamprey spawning behavior. Males and females typically mate with multiple partners, but mating is usually conducted one-on-one. First, the female anchors herself to a stone or other substrate with her sucker-like mouth. The male then uses his mouth to attach himself to the female's head, and wraps his lower body around the female's cloaca. Finally, the male induces egg excretion by shaking the lower half of the female's body. In this video, the second 'sneaker' male is also wrapped to the female.
Yamazaki C, Koizumi I. Journal of Ethology, January 19, 2017