a water mite.
2. water spider ·- any spider that habitually lives on or about the water, especially the large american species (dolomedes lanceolatus) which runs rapidly on the surface of water;
called also raft spider.
3. water spider ·- an aquatic european spider (argyoneta aquatica) which constructs its web beneath the surface of the water on water plants. it lives in a bell-shaped structure of silk, open beneath like a diving bell, and filled with air which the spider carries down in the form of small bubbles attached one at a time to the spinnerets and hind feet. called also diving spider.