LAUSR

Abstract A combination of morphological and genetic data (subunit I of the cytochrome c oxidase: COX1) was used to study the diversity and distribution of pseudotanaids in the Kuril-Kamchatka Trench and adjacent abyssal plain. Our results uncovered the presence of an undescribed species of Mystriocentrus (M. hollandae) and five new species of Pseudotanais (P. chanelae, P. monroeae, P. curieae, P. szymborskae and P. locueloae). The most abundant species was P. curieae (N = 182), followed by P. monroeae (N = 34), P. szymborskae (N = 31) and P. chanelae (N = 20). The number of individuals sampled was highest in shallower stations, but all four taxa could be found across the studied bathymetric range (4800–5500 m). Pseudotanaid abundance and bottom currents appear to be inversely related, which might be due to lower currents favouring sedimentation and, consequently, successful settlement of tanaids. Results are compared with previous studies on peracarid crustaceans from the Northwestern Pacific.