  The essential points and physical backgrounds of the covariant
level-classification scheme, recently proposed by us, are reviewed: In this
scheme the general composite hadrons are classified as the multiplets with the
U(12)SF * O(3,1) symmetry, where U(12)SF supset U(4)D.S. * SU(3)F, and U(4)D.S.
is a homogeneous Lorentz transformation group for Dirac spinors. This symmetry
predicts the existence of new type of chiral mesons and baryons out of the
conventional level classification scheme. The sigma nonet is a typical example
of chiralons to be assigned to the q bar q relativistic S-wave state.
