  Squirmers are models of a class of microswimmers, such as ciliated organisms
and phoretic particles, that self-propel in fluids without significant
deformation of their body shape. Available techniques for their simulation are
based on the boundary-element method and do not contemplate nonlinearities such
as those arising from the fluid's inertia or non-Newtonian rheology. This
article describes a methodology to simulate squirmers that overcomes these
limitations by using volumetric numerical methods, such as finite elements or
finite volumes. It deals with interface conditions at the squirmer's surface
that generalize those in the published literature. The actual procedures to be
performed on a fluid solver to implement the proposed methodology are provided,
including the treatment of metachronal surface waves. Among the several
numerical examples, a two-dimensional simulation is shown of the hydrodynamic
interaction of two individuals of Opalina ranarum.
