For educational purposes:
Information on the basics of Invertebrate Zoology
An Introduction To The Study of Invertebrate Zoology
Kingdom: Animalia, Phylum: Nematomorpha
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The Nematomorpha were previously known as the Gordiacea. They appear as Nematoda superficially, although internally they are considerably different. They do not have a lateral line or an excretory canal. Their nervous system consists of a dorsal brain and a single ventral cord. The genital ducts of both sexes open into the hindgut to form a cloaca. Development is unique with gastrulation by invagination and the larvae have a peculiar boring organ that infects insects. Their alimentary canal is usually degenerate and the body cavity may either contain parenchymous tissue or mostly empty of cells.
Borradaile & Potts (1958) discussed an example of he phylum, Gordius robustus. Adults of this species occur in streams during late autumn until late spring when they copulate. The sperm is not introduced directly into the cloaca, but rather is placed in masses on the body nearby. The eggs are laid in the water and the larvae hatch. They have a boring organ that allows them to find their way into the body cavity of crickets living nearby in the water. There they remain and grow until autumn when they leave their host and enter the water again as mature organisms.
Please see following plates for Example Structures of the Nematomorpha:
Plate 64 = Phylum: Nematomorpha -- Trichinella sp. = Gordian worms