A new species of Spirobrachia (Pogonophora) from the Orkney Trench (Antarctica)

Spirobrachia orkneyensis sp. nov. is described from the Orkney Trench to the east of the South Orkney Islands from a depth of 6130–6420 m. It differs from the congeneric species S. grandis (Ivanov 1952) and S. leospira (Gureeva 1975) in the structure of the tube, i.e. shorter segmental collars, peculiarities of their arrangement throughout the tube, and multi-layered, light-coloured tube wall with wrinkles in its inner layers. Also, the wings of the spermatophores of the new species are much larger than those of the two other species of the genus, while most other size characteristics, including the length of the spermatophores, the size of the cuticular plaques, the number of the tentacles and the diameter of the tube, are intermediate between those of S. grandis and S. leospira. A key to the genera and species of the family Spirobrachiidae is provided.