[xipho]

I know of Halobates, they live on top the ocean, not in the ocean. I.e. they have no adaptations to breathe in salt water. There are many other species like this that are restricted to tidal (flies, parasitic wasps, etc.) or costal areas and nowhere else, but again, not under water.

[andrewflnr]

Even their nymphs?

[xipho]

Right, they are not underwater. Hemimetaboulous insects like Holobates look like baby adults when they are born, and undergo multiple "partial" metamorphosis. In this case their wings are almost non-existent. They will go through multiple molts, gradually looking more like the adult. Holometabolous insects (e.g. beetles, wasps, butterflies, flies) are the ones with radically different body plans, often exploiting different niches, the larva could be aquatic, the pupa and adult terrestrial. Some more "basal" insects (dragonflies, mayflies) also have different body-plans at different stages, though instead of "larva" we say "imago", and things like that, for those lineages.