  The newly discovered exotic $\Theta$ baryon of mass 1540 MeV (and very small
width) truly has a very low mass, if it is a pentaquark system of even parity.
A schematic model in which the coherent interaction of $u\bar s$ and $d\bar s$
pairs leads to a very large residual (non-confining) attractive interaction is
introduced. This collective vibrational model accounts for the mass and small
decay width to the $KN$ channel, but yields a significant coupling to the
virtual $K^*N$ channel. The schematic model predicts an attractive
$\Theta$-nucleon interaction strong enough to bind a $\Theta$ particle to a
nucleus in a state that is stable against decay via strong interactions. The
discovery of $\Theta$-nuclei could be a definitive proof that the $\Theta$
parity is even.
