This is a really strange specimen. I would guess it's one of the dry caddis pupa that scoots across the surface of the water as a pupa rather than emerging right away. Its "wing pads
" sure don't look right, though. Maybe they're deformed and that's why I was able to find this one as a pupa in the first place. It also looks like it might be a caddis adult missing its wings, but since I found three of them, that kind of rules out such an anomalous maiming.
I found this one and one other on a midstream rock. The previous day, I caught a similar creature kicking around on the water's surface.
This one died and shriveled a little bit before I could photograph it, but it's basically in its original shape.