  The comprehensive low-temperature specific heat C(T) data identify both an
isotropic s-wave and an extended s-wave order parameters coexisting in a
superconducting single crystal FeSe with Tc=8.11 K. The isotropic gap
{\Delta}0=1.33 meV on the hole Fermi sheets and the extended s-wave gap
{\Delta}={\Delta}e(1+\alpha*cos2_theta) with {\Delta}e=1.13 meV and \alpha=0.78
on the electron Fermi sheets. The extended s-wave is rather anisotropic but the
low energy quasiparticle excitations demonstrate no sign of the accidental
nodes. The coefficient \gamma(H) manifesting the quasiparticle contribution to
C is a non-linear function of the applied magnetic field H in the mixed state
in accord with the anisotropic multi-order parameters.
