The research aimed to recollect specimens from Curaçao of the genus Halosbaena belonging to the rare crustacean order Thermosbaenacea, a genus with a relictual Tethyan distribution. It resulted in recording the apparent extinction of the entire, species-rich, subterranean fauna on the island that had occurred within a period of 43 years up to 2015. The composition of the groundwater fauna on Curaçao was sampled in 2015 for comparison with sampling undertake 43 years previously. Despite using the same sampling methods previously used and comprehensive coverage of the available sampling sites, no stygofauna specimen was collected from sampling in 2015 in contrast to more than 50 species collected from the initial sampling in 1973. It is hypothesised that this faunal extinction was associated with the oil industry, but it is unclear whether it resulted from petroleum pollution of groundwater drawdown or recharge. This record of the extinction of an entire ecosystem, rather than merely some members of it, is perhaps unique, but is concerning amongst the more diffuse extinction events happening globally.