The time-honored assumption about the defensive function of trichocysts in Paramecium against predators was recently verified experimentally against different species of unicellular predators. In the present study, we examined the defensive function of trichocysts against three metazoan predators, Cephalodella sp. (Rotifera), Eucypris sp. (Arthropoda), and Stenostomum sphagnetorum (Platyhelminthes). The results confirmed the defensive function of trichocysts against two of these metazoan predators (Cephalodella sp. and Eucypris sp.), while they seem ineffective against S. sphagnetorum. We also compared the defensive efficiency of the trichocysts of P. tetraurelia with that of toxin-containing extrusomes of two ciliates.