  In this talk, multiquarks are studied microscopically in a standard quark
model. In pure ground-state pentaquarks the short-range interaction is computed
and it is shown to be repulsive. An additional quark-antiquark pair is then
considered, and this is suggested to produce linear molecular system, with a
narrow decay width. The quarks assemble in three hadronic clusters, and the
central hadron provides stability. The possible crypto-heptaquark hadrons with
exotic pentaquark flavours, with strange, charmed and bottomed quarks, are
predicted.
