The slit spider, Fissarena ethabuka gen. et sp. nov. is described in the superfamily Clubionoidea. It builds an unusual retreat in the sand dunes of the Simpson Desert, Central Australia. The spider constructs a horizontal slit into consolidated sand. Behind the wide entrance is a gradually-narrowing, flat burrow. The steep top edge of the crack hangs over a slipface of loose sand at the mouth of the burrow, which serves as a trap for crawling prey, especially ants. Slit spiders were common, particularly on the dune crest, where 44% of the population occurred at a density of 0·2 m^-2. We suggest that the ubiquitous filamentous biogenic dune surface crust is crucial for the ability of this spider to construct such stable crevices in dune sand. Keywords: Araneae, Clubionoidea, new taxon, desert, slit burrow, sand trap, sand dunes, Australia.