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Nematomorpha

Nematomorpha (sometimes called Gordiacea, and commonly known as Horsehair worms or Gordian worms) are a phylum of parasitic animals which are morphologically and ecologically similar to nematode worms, hence the name. They are, on average, 1 meter long, and 1 to 3 millimetres in diameter. Horsehair worms can be discovered in damp areas such as watering troughs, streams, puddles, and cisterns. The adult worms are free living, but the larvae are parasitic on beetles, cockroaches, grasshoppers and crustaceans. About 320 species have been described.

Nematomorphs possess an external cuticle without cilia. Internally, they have only longitudinal muscle and a non-functional gut, with no excretory, respiratory or circulatory systems. Reproductively, they are dioecious, with the internal fertilization of eggs that are then laid in gelatinous strings.

Nematomorphs can be confused with nematodes, particularly Mermithid worms. Unlike Nematomorphs, 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.^[1]

In Spinochordodes tellinii, which has grasshoppers as its vector, the infection acts on the grasshopper's brain and causes it to seek water and drown itself, thus returning the nematomorph to water.^[2] They are also remarkably able to survive the predation of their host, being able to wriggle out of the predator which has eaten the host cricket.^[3]

Relationships within the phylum are still somewhat unclear, but two classes are recognised:

• Class Nectonematoida: 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
• Class 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

References

External links

• The cricket suicide (video)
• Videos of a cricket infected with a Gordian worm with the worm emerging to mate, as well as emerging from predators which have eaten the infected cricket. From Nature, April 2006.
• YouTube video of worms crawling out of a crushed grasshopper.