The scuba spider is the only spider known to live exclusively underwater. However, it does not have gills so how does it survive? It has created a unique way to create air sacs under the water in order to breathe.
The spider swims to the surface, collects an air bubble on its abdomen, swims back to its nest and leaves the air bubble intact. It then swims back up to get another air bubble. By doing this repeatedly, it creates a large air sac under the water that it can live off of for a length of time.