What is "water spider"

Water mite \Wa"ter mite`\ (Zo["o]l.) Any of numerous species of aquatic mites belonging to Hydrachna and allied genera of the family Hydrachnid[ae], usually having the legs fringed and adapted for swimming. They are often red or red and black in color, and while young are parasites of fresh-water insects and mussels. Called also water tick, and water spider.

n. diving bell spider