This “water walker” isopod, in the family Munnopsidae, was seen at a depth of 4,113 meters (2.6 miles) while exploring Rockaway Seamount on the fifth dive of the 2021 North Atlantic Stepping Stones expedition. It was one of several swimming invertebrates seen during the dive. We also saw polychaete worms, a swimming cucumber, and several shrimp-like mysids.