This species is the only spider in the world that spends its entire life under water (3). It has a number of adaptations for this aquatic life-style. The abdomen and legs are densely covered in short hairs that trap air when the spider is submerged (2). Although the spider is velvet-grey out of the water, when it is in the water the air trapped around its body gives it a silvery appearance, which has been likened to quick-silver (mercury) (1). This is one of the very few spiders in which the males are larger than the females (4). Although this species has been placed in a separate family, the Argyronetidae, recent scientific studies examining fossil spiders suggest that it should be placed in the family Cybaeidae (5).