Gordioida

Definition

A class of parasitic worms in the phylum Nematomorpha, commonly called horsehair worms. Gordioida contains the order Gordioidea (approximately 320 species) and is distinguished from the smaller class Chordodea by morphological and molecular characters. Adults are free-living in freshwater, while larvae develop inside terrestrial arthropod hosts—primarily insects such as crickets, grasshoppers, beetles, and mantids—eventually driving the host to water where the mature worm emerges to reproduce.

Etymology

From Gordius (type genus, named after the legendary Gordian knot, alluding to the tangled mass adults often form) + -oida (resembling), referring to the class's similarity to the type genus.

Example

A cricket infected with a gordioidan worm may exhibit aberrant behavior such as seeking water and jumping in, allowing the adult worm to emerge and complete its life cycle.

Related Terms

• Nematomorpha
• Gordioidea
• Chordodea
• horsehair worm
• Gordian worm
• Parasitic castration
• definitive host
• arthropod parasite

Usage Notes

The taxonomy of horsehair worms remains unsettled; some authorities treat Gordioida as a subclass or synonymize it with other groupings. The class contains primarily the large order Gordioidea, with Chordodea sometimes placed as a separate class or as an order within Gordioida. Specialists in nematomorph systematics should consult current molecular phylogenies, as ranks and composition have shifted in recent revisions. The common name 'horsehair worm' applies broadly to both classes.