They are tiny, transparent mites and worms - only a millimetre long and thinner than a human hair - but they may be big enough to throw a spanner in the works of a billion-dollar coal seam gas project.

Two previously unknown species of minuscule ''stygofauna'' have been discovered in aquifers beneath the site near Narrabri where resources company Santos hopes to drill the state's biggest gasfield.

Only a millimetre long: An unknown species of "stygofauna" discovered in aquifers.

The stygofauna are small enough to wander among grains of sand in the sandstone aquifers, never seeing the sun but purifying the water by eating bacteria - playing a similar role to earthworms in soil. Under the ''water trigger'' laws introduced into Federal Parliament by independent MP Tony Windsor, the discovery of new species could delay Santos' plans.

A leading hydrobiologist, Peter Serov, said the drilling plans had the potential to ''wipe out the entire community'' of little creatures. On Thursday his research was one of about 1800 public submissions to the federal government criticising aspects of the Santos plan to drill 18 wells on the Pilliga site, as a precursor to full-scale commercial gas production.