The phylum Nematomorpha (also known as horsehair worms) is comprised of two orders: Nectonematoidea (monogeneric (Nectonema), with four known species) and Gordioidea, in which the remainder of the over 300 described nematomorphan species are placed. There are 19 currently recognized genera within Nematomorpha, and estimates of global species diversity for this phylum are as high as 2,000. While Nectonema species are marine, planktonic worms, gordioids are found in freshwater, most commonly along the banks of ponds and streams, and some are semi-aquatic and live in damp soil. Nematomorphans are parasitic as larvae (Nectonema species parasitize marine invertebrates, while gordioids utilize terrestrial arthropods) and are free-living and aquatic as adults.