My hidden cukes did some glass crawling at night for a while after the LR arrived. They're settled in their hidey-holes now.
Here's what I think. Bristleworms move with their segmental parapodia, but they go fast. Nudis can have spikes, but don't move with them, so I'm ruling them out. Cukes have tube feet, which might look like the spikes votek describes, and they move painfully slowly.
Brilliant analysis, which will be disproven when we have a picture.