- Name Meaning: Thread form
- English Common Name: Horsehair worms, Gordian worms
- Major distinguishing characteristics:
- Approximate number of species described: about 320 known, about 2000 probable
The adult worms are free-living in freshwater, with the exception of 5 marine species known.
The larvae are parasitic on arthropods (such as insects and crustaceans). The larva cause the changes in the brain of the host that eventually cause the host to seek water and drown. The parasite then emerges into the water as an adult worm.
Adults sometimes congregate in balls, wrapping around one another.
There are two classes.
- Nectonematoida, which includes the 5 marine species in the genus Nectonema.
- Gordioida which includes two families of freshwater species
Horsehair worms range in length from 50 millimeters (2 in) to 2 meters (6 feet).
Their nervous system consists of a nerve ring that apparently serves as a brain near the "front", and a ventral nerve cord. There are no functioning digestive, circulatory or other systems.
The Fossil Record
Fossils resembling Nematomorpha have been found in the early Cambrian of China.