Antarctic intertidal zones are extremely harsh environments, and the Antarctic limpet Nacella concinna is one of the most conspicuous components of the macrofauna, colonizing such areas at King George Island, South Shetlands. The limpet subpopulation encompasses an intertidal and a subtidal ecomorph; these differ with respect to shell height and inner volume. We studied morphological, behavioural and physiological traits that distinguish both N. concinna subpopulations. We found a higher volume to circumference ratio of intertidal versus subtidal limpets to go along with a drastically reduced loss of body water during air exposure in intertidal specimens. Smaller intertidal limpets were less susceptible to desiccation than larger individuals. Further, the intertidal snails avoided accumulation of anaerobic metabolites (succinate, lactate and propionate), whereas subtidal limpets switched to anaerobic fermentation when exposed to air for >12 h. Only acetate accumulated in both types of snails after 12 h. Mean pO2 in shell water was higher in intertidal (2.6 kPa) than subtidal individuals (1.3 kPa) when submersed under water, and only the intertidal snails appeared able to respire air on emersion. These differences document strong physiological diversification between shore levels and shell morphs in the Antarctic limpet subpopulation at King George Island. © Inter-Research 2008.