  We show that the nodal quasiparticles have significant effect on the
classical phase fluctuations in a quasi-two-dimensional d-wave superconductor.
They give rise to singularities in the temperature behavior of some of the
coupling constants in the phase-only effective action. One of the consequences
is that the classical XY-model is not adequate for the description of the
superconducting fluctuations in d-wave superconductors at low temperatures.
