It is Argyroneta aquatica. This spider not only dive, but completes its entire life cycle underwater.
How does it breathe? It produces an air bubble that envelops the opisthosoma (the “body” without the “head”). As the bubble consumes, the spider comes to the surface to add other bubbles and increase its supply of air.
How is it fed? Taking advantage of aquatic plants, the spider forms a kind of silk bell, where it introduces bubbles, thus creating an air chamber. The spider must feed inside this air chamber, since it is fluidophagus and it could not emit the predigestive enzymes into the water because they would dissolve.