Swimming of the pea crab (Pinnotheres pisum)

Aquatic organisms have to deal with different hydrodynamic regimes, depending on their size and speed during locomotion. The pea crab swims by beating the third and fourth pereiopod on opposite sides as pairs. Using particle tracking velocimetry and high-speed video recording, we quantify the kinematics and vortices in the wake of the pea crab. Where the proximal parts of the pereiopods beat in antiphase, their distal parts show an overlapping beat period. By using four instead of two limbs for propulsion, an uninterrupted forward movement is established, reducing the influence of the acceleration reaction. Before body speed is maximal, force generation of the pereiopods seems most active when passing an orthogonal position with the body.