  We investigate, in the framework of a recently introduced new class of
invariant geometrical scalar-tensor theory of gravity, the possibility that a
viscous dark fluid can be described in a unified manner by a single scalar
field. Thus we developed a model in which both the metric tensor and the scalar
field have geometrical origin. The scalar field is characterized by a
non-canonical kinetic term and the scalar viscosity of the dark fluid appears
as soon the kinetic energy of the scalar field is no longer canonical. The
scalar viscosity is considered as a function of the Hubble and the deceleration
parameters. To illustrate the formalism we have considered two cases: a
constant and a thermodynamic equation of state parameters. In the both cases we
obtain analytic representations for the scalar field and their respective
potentials. We delimit free parameters by comparing with some Planck 2018
results.
