Gordian worms, horsehair worms

Code IJ999999

Key terminates here

Phylum Nematomorpha comprises two families ( Gordiidae, Code IJ019999 , Chordodidae, Code IJ029999 ) of very long, wiry, roundworm-like animals possibly related to nematodes. The juvenile stage is parasitic in insects or other arthropods. The non-feeding adult stage is aquatic. Adult Nematomorpha are circular in section, about 1-2 mm in diameter and 10-100 cm long. Known as horsehair worms (for their resemblance to a rather stout horsehair) or Gordian worms (for their habit of coiling into tangled masses of two or more individuals), they occur in small bodies of still freshwater and in moist soil at the edges of ponds.

Both families are reported from Australia. No genera are endemic. All records are from the eastern half of the continent (Williams, 1980).

Identification

Identification to phylum can be based on body form. The only possibility for confusion is with the nematode order Merminthida. Merminthids are similarly shaped, are generally shorter (to about 500mm long), and have a similar life history. Adult merminthids possess remnants of the mouthparts through which the juvenile feeds, and the intestine is developed into a fat-body.

Nematomorpha take food by absorption through the integument. The intestine is reduced and non-functional and the oesophagus is solid even when vestiges of mouthparts are present. Merminthids possess a typically nematode nervous system with ventral, dorsal and lateral nerve cords. In Nematomorpha, the somatic nervous system is reduced to a single ventral cord.

Identification to family can be based on a single character: the presence of numerous, well-defined areoles in the cuticle of Chordodidae, and their absence from Gordiidae. These areoles are small thickenings perforated by a pore, and often bearing setae, bristles or other structures.

Reference:

Williams, W.D. (1980) Australian Freshwater Life: The Invertebrates of Australian Inland Waters. The Macmillan Company of Australia, Melbourne.