Diversity out of simplicity: interaction behavior of land planarians with co-occurring invertebrates.

Land planarians have a simple anatomy and simple behavioral repertoire in relation to most bilaterian animals, which makes them adequate for the study of biological processes. In this study, we investigate the behavior of land planarians during interaction events with other invertebrates found in the same environment. We observed 16 different behavioral units, including seven different capture behaviors and three different prey ingestion behaviors. The capture behavior varied from very simple, such as simply covering the prey with the body, to more complex ones, including two forms of tube formation that are described for the first time. In general, the capture behaviors were similar among different predators but different for different prey. Similarly, prey ingestion type was more related to prey type than to predator species, with small soft prey being swallowed without fragmentation, large prey being crushed, and prey with a hard skeleton being perforated. Considering that land planarians face limitations due to their lack of efficient ways to retain water, thus being highly dependent on a moist environment, the set of behaviors shown by them in this study was considerably rich, especially concerning strategies to capture prey.