  The antisymmetry requirement of rishon bound state wave functions suggests a
new rishon quantum number called M spin. From M spin conservation and the
Nussinov-Weingarten-Witten theorem we predict the existence of a stable
pseudoscalar dirishonic meson, called zeta, that is lighter than the lightest
neutrino. Its mass is estimated as m(zeta) = 10^{-9} eV. This particle could
make up the major part of cold dark matter in the Universe.
