  We use a newly-developed method to identify local structural motifs in a
popular model glassformer, the Kob-Andersen binary Lennard-Jones mixture. By
measuring the lifetimes of a zoo of clusters, we find that 11-membered bicapped
square antiprisms, denoted as 11A, have longer lifetimes on average than other
structures considered. Other long-lived clusters are similar in structure to
the 11A cluster. These clusters group into ramified networks that are
correlated with slow particles and act to retard the motion of neighbouring
particles. The structural lengthscale associated with these networks does not
grow as fast as the dynamical lengthscale $\xi_4$ as the system is cooled, in
the range of temperatures our molecular dynamics simulations access. Thus we
find a strong, but indirect, correlation between static structural ordering and
slow dynamics.
