  Recent observations of HL Tau revealed remarkably detailed structure within
the system's circumstellar disc. A range of hypotheses have been proposed to
explain the morphology, including, e.g., planet-disc interactions, condensation
fronts, and secular gravitational instabilities. While embedded planets seem to
be able to explain some of the major structure in the disc through interactions
with gas and dust, the substructure, such as low-contrast rings and bands, are
not so easily reproduced. Here, we show that dynamical interactions between
three planets (only two of which are modelled) and an initial population of
large planetesimals can potentially explain both the major and minor banded
features within the system. In this context, the small grains, which are
coupled to the gas and reveal the disc morphology, are produced by the
collisional evolution of the newly-formed planetesimals, which are ubiquitous
in the system and are decoupled from the gas.
