nematomorph

Nematomorphs, also known as horsehair worms or gordian worms, are a phylum of invertebrates belonging to the superphylum Ecdysozoa. They are exclusively aquatic or semi-aquatic organisms. Adult nematomorphs are typically long and thread-like, with some species exceeding a meter in length, though their diameter is very small. They are often found in freshwater habitats such as ponds, streams, and puddles, as well as in some marine environments. Their coloration can vary, ranging from black and brown to white and translucent.

The life cycle of nematomorphs is complex and involves at least two hosts. Free-living, aquatic larvae are ingested by an arthropod intermediate host, typically an insect like a cricket or cockroach. Within the arthropod, the larva develops into a juvenile worm. The juvenile then manipulates the behavior of its host, often causing it to move towards water. Once the infected host enters the water, the juvenile nematomorph emerges and continues its development into an adult. Adults are free-living in water and do not feed, relying on stored reserves from their larval stage. Reproduction occurs in water, with females releasing eggs into the environment. Nematomorphs are often studied for their parasitic manipulation of host behavior.