  The observation of $Z_{cs}(3985)$ by BESIII in the $D_s^{*-}D^0$ and
$D_s^{-}D^{*0}$ channel adds important dynamic information for a coherent
understanding of both $Z_c(3900)$ and $Z_c(4020)$, as well as their strange
partners $Z_{cs}(3985)$ and $Z_{cs}(4120)$, on the basis of heavy quark spin
symmetry. With an overall short-ranged contact potential in SU(3) flavor
symmetry we show that the pole structures can be extracted from the
experimental data. Meanwhile, we show the key role played by the $S$-wave open
thresholds in $e^+e^-$ annihilations which are correlated with the production
of these $Z$ states in a hadronic molecule picture. Implications of their
scalar heavy quark spin partners $W_{c0,1,2}$ and $W_{cs0,1,2}$ are also
gained.
