  Quantum Chromodynamics presents a series of exact and approximate symmetries
which can be exploited to predict new hadrons from previously known ones. The
$Z_c(3900)$ and $Z_c(4020)$ resonances, which have been theorized to be
isovector $D^* \bar{D}$ and $D^* \bar{D}^*$ molecules [$I^G(J^{PC}) =
1^-(1^{+-})$], are no exception. Here we argue that from SU(3)-flavor symmetry,
we should expect the existence of strange partners of the $Z_c$'s with hadronic
molecular configurations $D^* \bar{D}_s$-$D \bar{D}_s^*$ and $D^*
\bar{D}^{*}_s$ (or, equivalently, quark content $c\bar{c} s \bar{q}$, with $q =
u, d$). The quantum numbers of these $Z_{cs}$ and $Z_{cs}^*$ resonances would
be $I(J^P)$ = $\frac{1}{2}(1^+)$. The predicted masses of these partners depend
on the details of the theoretical scheme used, but they should be around the
$D^* \bar{D}_s$-$D \bar{D}_s^*$ and $D^* \bar{D}^{*}_s$ thresholds,
respectively. Moreover, any of these states could be either a virtual pole or a
resonance. We show that, together with a possible triangle singularity
contribution, such a picture nicely agrees with the very recent BESIII data of
the $e^+e^-\to K^+(D_s^-D^{*0}+D_s^{*-}D^0)$.
