A new Entoprocta species from the northwestern Weddell Sea shelf (Southern Ocean), its soft-sediment habitat and possible polychaete hosts

Abstract Rare meiofauna taxa are often indicators of specific environmental conditions. A new and rare species of Entoprocta from the Southern Ocean, its abundance, habitat and possible commensal relationship with Polychaeta are presented. During the RV Polarstern expedition PS118 (2019) to the northwestern Weddell Sea, sediment samples were taken with a multicorer. The species of the family Loxosomatidae was discovered in the meiofauna size fraction of samples of only one of three investigated stations (413–415 m depth). Loxosomella sigridae sp. nov. is a solitary, medium-sized entoproct (total length up to 773 µm). Decisive characters of the adult include twelve tentacles, an aborally situated Y-shaped cell row, paired accessory gland cells along the foot groove and smooth adhesive papillae at the tip of the foot. The reproductive cycle of Loxosomella sigridae sp. nov. has a sexual and an asexual phase via larvae and bud-carrying individuals, respectively. We present confocal laser-scanning images of both developmental stages. Integrative methods are used to describe the habitat of Loxosomella sigridae sp. nov. and gain insight in its relationship to possible host organisms. We discuss co-occurring polychaete families and their ecology and conclude that Cirratulidae and/or Paraonidae may most likely be the hosts of Loxosomella sigridae sp. nov.