English: Horsehair worms; Gordian worms.
Synonym: Nematomorphs; Gordiaceae.
Name: Gordian from living in knots.
Members: 326 known species; estimate of 2000 species worldwide.
Habitat: damp areas, watering troughs, swimming pools, streams, puddles, and cisterns.
ZoologyWorms; parasitoid; adults are free living, larvae are parasitic on beetles, cockroaches, grasshoppers, crustaceans; similar to nematodes; 50 to 200 centimetres long; 1 to 3 millimetres diameter
Body: an external cuticle without cilia; only longitudinal muscle; non-functional gut; no excretory, respiratory or circulatory systems. Reproduction: dioecious, with the internal fertilization of eggs that are then laid in gelatinous strings.
Larvae: have rings of cuticular hooks and terminal stylets.
Adults: mostly free living; males and females aggregate into tight balls (Gordian knots) during mating.
TaxonomyNematomorphs is placed in the Phylum Ecydosoa, with moulting organisms like
Arthropoda.
Nematomorphs can be confused with nematodes, particularly Mermithid worms. Mermithids do not have a terminal cloaca. Male mermithids have one or two spicules just before the end apart from having a thinner, smoother cuticle, without areoles and a paler brown colour.
ClassesNectonematoida: marine, planktonic, with a double row of natotory setae along each side of the body; with dorsal and ventral longitudinal epidermal cords, blastocoelom spacious and fluid filled; gonads single; larvae parasitise decapod crustaceans.
Gordioidea: freshwater and semiterrestrial; lack lateral rows of setae; with a single, ventral epidermal cord; blastocoelom filled with mesenchyme in young animals but becomes spacious in older individuals; larvae parasitise grasshoppers and crickets.