Including those that float on it (epineuston) or under it (hyponeuston) -- including larger ones such as insects and more microscopic protozoa and bacteria. This being a boundary environment, it's a particularly varied ecosystem. Sometimes the word is specifically used to mean those that rely on surface tension to maintain their position, but it can also be used of, say, flying fish. The word was adopted in the mid-1920s from German, where it was coined from Greek neustós, those who swim.
The mosquito broke out of the neuston and flew away.