The spermatozeugmata of Tubifex tubifex are bundles of spermatozoa, stored in the spermathecae and composed of two types of sperm cells. The eupyrene, fertilizing, spermatozoa are stored parallel to the central axial cylinder, whereas the oligopyrene spermatozoa are helically arranged in the cortex. The main portions of their tails are connected by a junctional complex. When placed in Ringer solution the free extremities of the oligopyrene sperm tails start beating with metachronal waves, forming a series of wave fronts that are helically arranged around the spermatozeugma. The wavelength is 2.76 μm and the beat frequently is around 10 Hz. Besides the functions already suggested for the spermatozeugmata (holding together fertilizing spermatozoa; selecting nutrients from the lumen of the spermatheca) another function is proposed: the oligopyrene sperm tails, which form the helical metachronal wave, may help the transport of the spermatozeugma from the spermatheca to the opening of the spermathecal duct.