On the сomplexity of quasivariety lattices

We prove that any AD-class of algebraic structures of finite signature contains continuum many proper subclasses, which have the Nurakunov non-computability property, but which are not Q-universal (among those are almost all the known Q-universal quasivarieties nowadays). A similar result holds for some classes of algebraic structures of countable signature. This provides a negative answer to an open question.