Cave nematodes. Light microscopy footage of nematode worms from a biofilm found in a cave. The biofilm was covering waters in Movile Cave, Romania. Movile Cave, located close to the Black Sea coast, was discovered in 1986. It consists of a network of fissures and small caves, flooded by mineral-rich waters. This forms a unique ecosystem that is low in oxygen but rich in hydrogen sulphide. Life here has evolved in isolation for millions of years, and microbes obtaining energy from hydrogen sulphide form the basis of the food chain.