Statistical and mechanical analysis of multi-pseudopodial locomotion in a testate amoeba, Arcella sp.

Adherent eukaryotic cells typically exhibit amoeboid locomotion through actin polymerization and bleb-driven mechanisms. However, testate amoebae, which enclose their bodies within a shell, exhibit variation in these locomotion types. This study focused on Arcella, a representative testate amoeba that pulls its shell using multiple pseudopods extending from a single aperture on the ventral side. Arcella is found in peatlands and freshwater, where it adapts its movement to various substrates. We characterized its movement on glass as well as hard, and soft gel substrates through detailed observation. The results indicated a higher randomness in motion on the soft gel, which was influenced by the pseudopodial elongation direction. Additionally, we evaluated the relationship between movement direction and traction stress. The dipole moment of the traction stress field determined the axis of motion, whereas quadrupole moments were correlated with forward and lateral movements. Although some relationships between multipole moments and velocity were shared with other cells, Arcella exhibited unique characteristics in its movement mechanism, which likely occurred due to its use of multiple pseudopods alongside its shell.