Generally speaking, nematomorphans are found in aquatic or occasionally terrestrial (either as semi-aquatic individuals themselves or within terrestrial hosts) environments throughout the world. They are known from every continent, with the exception of Antarctica. Gordioids are found in freshwater streams and ponds as adults (a few are found in damp soil) and most typically in terrestrial insects, as parasitic larvae. They are known from the waters of Indonesia, Japan, New Zealand, the Northern Atlantic, and the Mediterranean. Nectonema species are found in coastal, marine, and pelagic environments as adults, and are found as parasites in decapod crustaceans as larvae. ( Brusca and Brusca, 2003 Hanelt, et al., 2013 Poinar Jr., 2008 Schmidt-Rhaesa, 2012 Shapiro, 2012) Geographic Range Nematomorphans are parasitic as larvae ( Nectonema species parasitize marine invertebrates, while gordioids utilize terrestrial arthropods) and are free-living and aquatic as adults.

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.

There are 19 currently recognized genera within Nematomorpha, and estimates of global species diversity for this phylum are as high as 2,000. 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.

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