Swimming of \textit{Vorticella} in two-dimensional confinements

\textit{Vorticella }is a ciliate observed in the stalked sessile form (trophont), which consists of an inverted bell-shaped cell body (zooid) and a slender stalk attaching the zooid to a substrate. Having circular cilia bands around the oral part, the stalkless zooid of \textit{Vorticella} can serve as a model system for microorganism swimming. Here we present how the stalkess trophont zooid of \textit{Vorticella} swims in two-dimensional confined geometries which are similar to the Hele-Shaw cell. Having harvested stalkless \textit{Vorticella} zooids, we observed their swimming in water between two glass surfaces using video microscopy. Based on measured swimming trajectories and distributions of zooid orientation and swimming velocity, we analyzed how \textit{Vorticella}'s swimming mobility was influenced by the geometry constraints.