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Two examples of magnetic anti-dynamos in magnetohydrodynamics (MHD) aregiven. The first is a 3D metric conformally related to Arnold cat fast dynamometric: ${ds_{A}}^{2}=e^{-{\lambda}z}dp^{2}+e^{{\lambda}z}dq^{2}+dz^{2}$ isshown to present a behaviour of non-dynamos where the magnetic fieldexponentially decay in time. The curvature decay as z-coordinates increaseswithout bounds. Some of the Riemann curvature components such as $R_{pzpz}$also undergoes dissipation while component $R_{qzqz}$ increases without bounds.The remaining curvature component $R_{pqpq}$ is constant on the torus surface.The other anti-dynamo which may be useful in plasma astrophysics is the thinmagnetic flux rope or twisted magnetic thin flux tube which also behaves asanti-dynamo since it also decays with time. This model is based on theRiemannian metric of the magnetic twisted flux tube where the axis possessesFrenet curvature and torsion. Since in this last example the Frenet torsion ofthe axis of the rope is almost zero, or the possible dynamo is almost planar itsatisfies Zeldovich theorem which states that planar dynamos do not exist.Changing in topology of this result may result on a real dynamo as discussed.

Dynamos and anti-dynamos as thin magnetic flux ropes in Riemannian spaces