  We study swimming of small spherical particles who regulate fluid flow on
their surface by applying tangential squirming strokes. We derive translational
and rotational velocities for any given stroke which is not restricted by axial
symmetry as assumed usually. The formulation includes inertia of both the fluid
and the swimmer, motivated by inertia's relevance for large Volvox colonies. We
show that inertial contribution to mean speed comes from dynamic coupling
between translation and rotation, which occurs only for strokes that break
axial symmetry. Remarkably, this effect enables overcoming the scallop theorem
on impossibility of propulsion by time-reversible stroke. We study examples of
tangential strokes of axisymmetric travelling wave, and of asymmetric
time-reversible flapping. In the latter case, we find that inertia-driven mean
speed is optimized for flapping frequency and swimmer's size which fall well
within the range of realistic physical values for Volvox colonies. We
conjecture that similarly to Paramecium, large Volvox could use time-reversible
strokes for inertia-driven swimming coupled with their rotations.
