Pill millipedes are any members of two living (and one extinct)
orders of
millipedes, often grouped together into a single
superorder,
Oniscomorpha. The name Oniscomorpha refers to the millipedes' resemblance to certain
woodlice (Oniscidea), also called pillbugs or "roly-polies". However, millipedes and woodlice are not closely related, belonging to the
subphyla Myriapoda and
Crustacea, respectively.