  We propose a minimal model of microswimmer based on immersed boundary
methods. We describe a swimmer (either pusher or puller) as a distribution of
point forces, representing the swimmer's flagellum and body, with only the
latter subjected to no-slip boundary conditions with respect to the surrounding
fluid. In particular, our model swimmer consists of only three beads (two for
the body and one for the flagellum) connected by inextensible and rigid links.
When the beads are collinear, standard straight swimming is realized and, in
the absence of propulsion, we demonstrate that the swimmer's body behaves as an
infinitely thin rod. Conversely, by imposing an angle between body and
flagellum the swimmer moves on circular orbits. We then discuss how two
swimmers, in collinear or non-collinear geometry, scatter upon encounter.
Finally, we explore the dynamics of a large number of swimmers reacting to one
another only via hydrodynamic interactions, and exemplify their complex
collective dynamics in both straight and circular swimmers.
