  We investigate the fluid dynamics of brine shrimp larvae swimming in this
gallery of fluid motion video. Time resolved particle image velocimetry was
performed using nano-particles as seeding material to measure the time
dependent velocity and vorticity fields. The Reynolds number of the flow was
roughly 8 and the Womerseley number (ratio of periodic forcing to viscous
forcing) was about 5. Vorticity dynamics reveals the formation of a vortex ring
structure at the tip of each arm at the beginning of the power stroke. This two
vortex system evolves dramatically with time as the stroke progresses. The
outer circulation is noted to weaken while the inner circulation strengthens
over the power stroke. The gaining strength of the inner vortex correlates with
the acceleration and forward movement of the larvae.
