  We present fluid dynamics videos of the pulsing dynamics and the resulting
fluid flow generated by the upside down jellyfish, Cassiopea spp. Medusae of
this genus are unusual in that they typically rest upside down on the ocean
floor and pulse their bells to generate feeding currents, only swimming when
significantly disturbed. The pulsing kinematics and fluid flow around these
upside down jellyfish is investigated using a combination of videography, flow
visualization, and numerical simulation. Significant mixing occurs around and
directly above the oral arms and secondary mouths. Numerical simulations using
the immersed boundary method with a porous layer representing the oral arms
agree with the experimental results. The simulations also suggest that the
presence of porous oral arms induce net horizontal flow towards the bell.
Coherent vortex rings are not seen in the wake above the jellyfish, but
starting and stopping vortices are observed before breaking up as they pass
through the elaborate oral arms (if extended).
