  Thermal shifts and fluctuations at finite temperature below the deconfinement
crossover of QCD from hadronic matter to the Quark-Gluon Plasma provide a
viable way to look for exotic and missing states with given quantum numbers in
the hadronic spectrum. We study a realization of the Hadron Resonance Gas model
in the light quark ($uds$) flavor sector of QCD to study: i) the entropy
shifts, and ii) the fluctuations of electric charge, baryon number and
strangeness; and extract from them the possible existence of missing and exotic
states from a comparison with lattice data. The analysis of the entropy shift
based on the free energy of the Polyakov loop suggests the existence of exotic
hybrids $g q \bar q$ and $gqqq$.
