  The possibility of the $^8$He and $^{9}$Li clusters in atomic nuclei is
discussed. Until now most of the clusters in the conventional models have been
limited to the closures of the three-dimensional harmonic oscillators, such as
$^4$He, $^{16}$O, and $^{40}$Ca. In the neutron-rich nuclei, however, the
neutron to proton ratio is not unity, and it is worthwhile to think about more
neutron-rich objects with $N>Z$ as the building blocks of cluster structures.
Here the nuclei with the neutron number six, which is the subclosure of the
$p_{3/2}$ subshell of the $jj$-coupling shell model, are assumed to be
clusters, and thus we study the $^8$He and $^9$Li cluster structures in
$^{16}$Be ($^8$He+$^8$He), $^{17}$B ($^8$He+$^9$Li), $^{18}$C ($^9$Li+$^9$Li),
and $^{24}$C ($^8$He+$^8$He+$^8$He). Recent progress of the antisymmetrized
quasi cluster model (AQCM) enables us to utilize $jj$-coupling shell model wave
functions as the clusters rather easily. It is shown that the $^8$He+$^9$Li and
$^9$Li+$^9$Li cluster configurations cover the lowest shell-model states of
$^{17}$B and $^{18}$C, respectively. To predict the cluster states with large
relative distances, we increase the expectation value of the principal quantum
numbers by adding the nodes to the lowest states under the condition that the
total angular momentum is unchanged (equal to $J^\pi =0$). As a result,
developed cluster states are obtained around the corresponding threshold
energies. The rotational band structure of $^{24}$C, which reflect the symmetry
of equilateral triangular configuration ($D_{3h}$ symmetry) of three $^8$He
clusters, also appears around the threshold energy.
