  Jellyfish - majestic, energy efficient, and one of the oldest species that
inhabits the oceans. It is perhaps the second item, their efficiency, that has
captivated scientists for decades into investigating their locomotive behavior.
Yet, no one has specifically explored the role that their tentacles and oral
arms may have on their potential swimming performance, arguably the very
features that give jellyfish their beauty while instilling fear into their prey
(and beach-goers). We perform comparative in silico experiments to study how
tentacle/oral arm number, length, placement, and density affect forward
swimming speeds, cost of transport, and fluid mixing. An open source
implementation of the immersed boundary method was used (IB2d) to solve the
fully coupled fluid-structure interaction problem of an idealized flexible
jellyfish bell with poroelastic tentacles/oral arms in a viscous,
incompressible fluid. Overall tentacles/oral arms inhibit forward swimming
speeds, by appearing to suppress vortex formation. Non-linear relationships
between length and fluid scale (Reynolds Number) as well as tentacle/oral arm
number, density, and placement are observed, illustrating that small changes in
morphology could result in significant decreases in swimming speeds, in some
cases by downwards of 400% between cases with to without tentacles/oral arms.
