Worms aint just worms. There are flat worms, round worms and ringed worms (like the common earth worm). My flat worm (or slime worm), is a terrestrial planarian - there are many more planarians that live in the sea - and its mouth is on the underside of its body. There are quite a few different species of planarian in Australia including some introduced species that have probably hitched a ride on potplants. They come in a variety of colours and are carnivorous, venturing out at night to feed on earth worms and slugs . They are also hermaphrodites and can also reproduce asexually.
This flat worm is possibly Australoplana sanguinea, the same flat worm that has been discovered in southern England and Ireland in the last decade or so, introduced from eastern Australia.