Two new species of Princaxelia (Crustacea, Amphipoda, Pardaliscidae) from hadal depths of the Tonga and Mariana trenches (Pacific Ocean)

Princaxelia Dahl, 1959, is a genus containing predatory pardaliscid amphipods, typically captured in small numbers from hadal trenches (> 6,000 m ocean depth). Here, two new species, Princaxelia malohi Duffy & Wainwright, sp. nov. and Princaxelia kahat Duffy & Wainwright, sp. nov., are added to the genus based on key morphological features to bring the total number of species of Princaxelia to seven. DNA barcodes at the 16 S and COI region are also provided for all type specimens where possible to add to the limited but growing number available.

Princaxelia malohi sp. nov. was described from five specimens captured using baited landers between 8,200 –8,350 m water depth in the Tonga Trench. They exhibit the first identified record of Princaxelia from this hadal feature. Key diagnostic features include the presence of two plumose setae on the inner plate of maxilla 1 and one projection near the base of the dactylus in gnathopods 1 and 2.

The second species, Princaxelia kahat sp. nov., is described from between 8,000 –8,964 m in the Mariana Trench, and is the second species described from this hadal feature. Key diagnostic features for this species include the presence of six plumose setae on the inner plate of maxilla 1, and three to four projections near the base of the dactylus in gnathopod 1, and four to five projections on the base of the dactylus in gnathopod 2.

A morphological matrix and key to the genus is updated to aid in future identification of species of Princaxelia and notes on in situ observations are also included.