Critter is mostly black with tan wing suit around the periphery. The wing suit is not between the legs which it extends as required to move. Body about 5mm diameter (it is quite round) and nearly 10mm long including the antennae. It is quite hard and resists a press with thumb pad but yields to a thumb nail. Quite easy to catch, but can move quite rapidly when disturbed and given time to extend legs. It resembles in many ways a scale insect but does not feed like a scale insect on sap, rather it munches down on the thin leaf tissues between the veins leaving fairly large round holes and leaves skeletonized. It does not appear to be in the usual published lists of tomato bugs, so maybe it normally feeds elsewhere and for this season is holidaying in my tomato patch or it is just a juvenile stage of some more familiar pest.
I'll see if I can find it munching down on anything else locally. Located in Ontario, Canada.