Nematomorpha (sometimes called Gordiacea, and commonly known as horsehair worms or Gordian worms) is a phylum of parasitic animals that are superficially morphologically similar to nematode worms, hence the name. They range in size in most species from 50 to 100 centimetres (20 to 39 in) long and can reach in extreme cases up to 2 metres, and 1 to 3 millimetres (0.039 to 0.12 in) in diameter.