The genus Princaxelia, Pardaliscidae, is a rarely recorded, infrequently collected and hitherto observed benthic amphipod, typically found at hadal depths (>6000 m) in the Pacific Ocean trenches. Little is known about the behaviour or physiology of this genus. Using a baited camera lander, observations of Princaxelia jamiesoni were made in the Japan Trench (7703 m) and Izu–Ogasawara Trench (9316 m) and of Princaxelia aff. abyssalis in the Kermadec Trench (7966 m) and Tonga Trench (8798 m). These amphipods rapidly intercepted the bait and preyed upon smaller lysianassoid amphipods. Mean absolute swimming speeds for P. jamiesoni and P. aff. abyssalis were 4.16 cm.s−1 ± 1.8 SD and 4.02 cm.s−1 ± 0.87 SD respectively. These amphipods have the capacity for long range swimming, high manoeuvrability in close range, and efficient predatory behaviour. Burst swimming speeds for P. aff. abyssalis were 9 and 10 cm.s−1 with accelerations up to 22–25 cm.s−2.
