Carl,
the broad fan-like distribution of dust lanes at the end of the much shorter & broader of the two principal Luminous arms of M66, is well shown in your image. At very high contrast, one interpretation of the
three-dimensional geometry of this broadened and "smeared-looking" Arm is that the arm itself has been lifted out of the principal plane of this galaxy, perhaps by forces that originated in a previous encounter with the nearby galaxy NGC 3628 (
which is also a peculiar galaxy!!)
There are also other evidences for a previous encounter of M66 with NGC 3628 :
for instance there is an outermost very-very-faint arm-like feature (that could be a tidal arm) in M66, and there exists a bridge of HI (cold & neutral Atomic Hydrogen gas) between M66 and N3628.
Here is what M66 looks like, when imaged with a radio telescope at 21 cms, from The HI Nearby Galaxies Survey (Walter et al, 2008). This image shows
only the cold neutral atomic gas found in the galaxy M66:
The strong broadening of one of the two gaseous arms, and its much more chaotic morphology, is strongly suggestive of the idea that M66 has been perturbed!!
cheers, madbadgalaxyman