Clinging onto Arctic Benthos: Biogeography of Amathillopsis spinigera Heller, 1875 (Crustacea: Amphipoda), including its redescription

Amathillopsis spinigera Heller, 1875 , is an enigmatic peracarid crustacean species found in the Arctic Ocean. During the summer of 2024, it was recorded in the HAUSGARTEN observatory for the first time, following 25 years of regular sampling as part of the Fram Strait Long-Term Ecological Research program. This study significantly broadens the known geographic and bathymetric range of A. spinigera , with a total of 46 specimens collected from HAUSGARTEN (HG) and cold seeps at Svyatogor Ridge, during two expeditions conducted in 2024. Further, our review of all publicly available database (historical) records for A. spinigera leads to an expansion of its depth range from 186 – 1972 m to 11 – 3182 m. Recent observations using Remotely Operated Vehicles (ROVs) have confirmed their clinging behavior on organic structures such as worm tubes, likely elevating the species within the water column to facilitate food capture. Females at various life stages, including egg-bearing individuals, were observed alongside juveniles and males of different sizes, enabling a redescription of the species based on an integrative taxonomy approach that incorporates both molecular and morphological data. The study also highlights biogeographic patterns, with a notable preference for eastern occurrences along the Arctic continental slope. While gaps in data from Greenland and Canadian regions, coupled with minimal sampling in the Central Arctic Ocean, suggest potential sampling bias, circumarctic connectivity appears plausible. This inference is supported by high genetic similarity in barcode data from individuals found across distant geographic locations.