  We examine SU(3) constraints on the spectrum and decay widths of cryptoexotic
nucleon-like states in antidecuplet of pentaquarks. We show that in the ideal
mixing scenario the number of free matrix elements describing splittings
reduces from 4 to 2. Model-independent sum rules are derived.
  Using as input $\Theta^+$ and $\Xi_{3/2}$ masses we show that it is difficult
to interpret Roper and $N^{\ast}(1710)$ nucleon resonances as cryptoexotic
pentaquarks. Large $N_c$ limit for antidecuplet and accompanying octet in the
diqaurk picture and the analogy with the soliton model is also discussed.
