Eurythenes sigmiferus and Eurythenes andhakarae (Crustacea: Amphipoda) are sympatric at the abyssal Agulhas Fracture Zone, South Atlantic Ocean, and notes on their distributions

Cryptic species in the deep ocean are rapidly being identified with molecular evidence and as a result, new species are being described. Consequently, our understanding of distributions among the revised landscape of species needs to be reassessed. A model example is the large scavenging amphipod, Eurythenes gryllus (Lichtenstein in Mandt, 1882), which historically was thought to have a eurybathic and cosmopolitan distribution. Molecular evidence has since led to the separation of E. gryllus into ten named species and truncating its range to bi-polar bathyal depths. This study focuses on two species; Eurythenes sigmiferus and Eurythenes andhakarae d'Udekem d'Acoz and Havermans, 2015, and presents new records of both species from 5,493 m in the previously unsampled Agulhas Fracture Zone, South Atlantic Ocean (42.77°S, 10.05°E). We paired morphology with DNA barcoding at two mitochondrial regions to achieve robust identification and assessed their wider geographic range by reassessing historical records. Their overlapping presence at the Agulhas Fracture Zone expands their known ranges to the non-polar South Atlantic Ocean. Specifically, for E. sigmiferus, the data suggests this species has a multi-ocean tropical to temperate distribution from abyssal to shallow hadal depths (3,410–6,097 m). Eurythenes andhakarae is not restricted to the Southern Ocean but is distributed across the Antarctic Polar Front to the temperate South Atlantic Ocean between abyssal and hadal depths (3,069–7,099 m), with a presence at bathyal depths requiring molecular confirmation. This study highlights that pairing new expeditions with a re-inspection of rich historical collections exploration can fill in data gaps across species ranges and, ultimately, biogeography.