The discovery and subsequent observation over various years of a massive population of the thermosbaenacean Tethysbaena ophelicola Wagner in the subterranean karstic sulfide pool of Ayyalon (Israel) enabled us to reach conclusions about the previously unknown life strategy of this crustacean super-order. These are preferably monophagous sulfur-bacteria-eating pelagic shrimps of stratified subterranean pools, adapted to microaerobic-anaerobic conditions, by among others ovoviviparity and the probable help of sulfide detoxifying bacterial endosymbiosis.