Where polar ice sheets meet the coast, they can flow into the sea as floating ice shelves. The seabed underneath is in complete darkness, and may be Earth’s least known surface habitat. Few taxa there have been fully identified to named species (see Supplemental information) — remarkable for a habitat spanning nearly 1.6 million km2. Glimpses of life there have come from cameras dropped through 10 boreholes, mainly at the three largest Antarctic ice shelves — the Ross (McMurdo), Filchner-Ronne and Amery. Pioneering studies of life under boreholes found distinct morphotypes of perhaps >50 species. Here, we report remarkable growth and persistence over thousands of years of benthic faunal species collected in 2018 from the seabed under the Ekström Ice Shelf (EIS), Weddell Sea.