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Family Dytiscidae
This creature has gray plates and possibly six legs but no promises. It has large thin pincers in the front and possibly a stinger off its tail which it undulates to get through the water. They also bite each other.
Small Pond
These are diving beetle larvae. I can't even begin to guess which species, but I rear a species at work and their larvae look a lot like these. It appears as though you've got one eating another in both of your shots. That happens in close quarters, and that's the main reason I rear the larvae in separate containers! Great spotting.
Those might be dragonfly nymphs: http://www.dragonfly-site.com/dragonfly-...