A lock-on system in precopulae of Dikerogammarus villosus (Sowinsky, 1894), also present in Gammarus pulex pulex (Linnaeus, 1758) (Amphipoda): Amphipod Pilot Species Project (AMPIS) Report 2

In Dikerogammarus villosus and Gammarus p. pulex, a lock-on mechanism for amplexus was found. Large pores on the first and fifth female pereionites are involved, as well as the first pair of male gnathopods. On the anterior edge of pereionite 1 and the posterior edge of pereionite 5, specialized areas were found that allow penetration of the male's dactyli in the inter-segmental spaces of the female. Also, a guidance system for male attachment to the female was found using palmar spines of the first pair of gnathopods. The mechanism is described and discussed. Morphometric analysis of this lock-on system explains the strong size-relationship between partners