  Anisotropic viscous drag is usually believed to be a requirement for the low
Reynolds number locomotion of slender bodies such as flagella and cilia. Here
we show that locomotion under isotropic drag is possible for extensible slender
bodies. After general considerations, a two-ring swimmer and a model
dinoflagellate flagellum are studied analytically to illustrate how
extensibility can be exploited for self-propulsion without drag anisotropy.
This new degree of freedom could be useful for some complex swimmer geometries
and locomotion in complex fluid environments where drag anisotropy is weak or
even absent.
