A few months back I pond (well lake) dipped at a private nature reserve trying to get some dragonfly nymphs. I failed to find any, but did find some excellent saucer bugs, something I had only seen twice before.
They are true bugs (Heteroptera), which also includes the water boatmen, pond skaters and water scorpions, the distinctive feature of which are their needle like stabbing mouthparts.
They breathe air like all of the aquatic heteroptera, and take a bubble of air underwater, trapped on their undersides by tiny hairs.