Location of the studied area. A Cantabrian Mountains (northern Spain) B UTM grid map with 10 km squares of the central region of the Cantabrian Mountain to show the outcrops of the rock systems (in grey) which contain limestone and geographical situation of the study area with the distribution of the cave-dwelling Pseudosinella altamirensis sp. nov.: (1) Cudón cave; (2) La Venta del Cuco cave; (3) Altamira and Stalactites caves; (4) Peña Caranceja cave; (5) Cobezo cave. Source: Spanish Geological Institute and Cartographic Service of the Cantabrian Government, scale 1:50 000.