Tergipes antarcticus (Gastropoda, Nudibranchia): distribution, life cycle, morphology, anatomy and adaptation of the first mollusc known to live in Antarctic sea ice

Tergipes antarcticus (Gastropoda, Nudibranchia) has been reported from Antarctic sea ice twice (1903 and 2008). The extent of its distribution and life history remained unclear. We have evaluated data from several cruises, showing that T. antarcticus is widely distributed in sea ice throughout the Weddell Sea. Adults, juveniles, larvae and egg clutches of T. antarcticus were found in the ice indicating that the species reproduces within this habitat. We collected live material of T. antarcticus for a thorough description of all life stages and to investigate the developmental stages and physiological adaptations. Total developmental time from egg to veliger larvae was relatively short with 31 days (range 13-65 days) at 0 degrees C. Liquid withdrawn from egg clutches and adult T. antarcticus showed clear signs of thermal hysteresis. This is the first report of thermal hysteresis from a sea ice metazoan. We conclude that T. antarcticus is an autochthonous species to Antarctic sea ice.