Not Too Big for Its Mouth: Direct Evidence of a Macrodasyidan Gastrotrich Preyed in Nature by a Dileptid Ciliate

Nearly ubiquitous and usually speciose in most aquatic habitats, the meiofaunal-sized gastrotrichs are recognized as an important component of marine and freshwater ecosystems. The common observations that gastrotrichs feed on bacteria, microalgae and biodetritus strongly imply that they play a relevant role in linking the microbial loop to the higher trophic levels. Which are the organisms that in turn prey on gastrotrichs is, however, a substantially unexplored question. Inspecting meiofauna samples collected from shallow sites of the Tyrrhenian coast, we had the chance to spot a wild case of a macrodasyidan gastrotrich predated by a dileptid ciliate. This case is documented here with a set of in-vivo photos, jointly with an unequivocal taxonomic identification of the preyed gastrotrich with Paraturbanella teissieri and a tentative identification of the predator ciliate with Pseudomonilicaryon marinus.