OK, you've sold me on it. It seems awkward, so maybe they should be secondary weapons or something. And add in something like barbed defense?
OK, it seems we're agreed on making them a secondary attack. Same damage as for the spiny defense or a bit less?
Wouldn't it just go up with size advancement as usual? But I'd be happy to go with 1d12+Con or even 2d12 if you wanted for spiny defense.
Oh. Hmmm. That seems a bit awkward, and I'd think we'd have to do a table, so the damage levels off if the stepping creature is so large that its foot is bigger than the ray.
You know, I'm just not feeling it. I'm going to guess that other critters with spiny/barbed defense has similar "attacks per size" mechanisms originally that got removed in 3.X. In fact, I'm pretty sure we did that for some hazards, though I don't think any of our "recent" hazard conversions ever made it to the actual CC, which means I can't search easily.