Nematomorpha are a phylum of parasitoid animals superficially similar to nematode worms in morphology, hence the name. Most species range in size from 50 to 100 millimetres long, reaching 2 metres in extreme cases, and 1 to 3 millimetres in diameter. Horsehair worms can be discovered in damp areas, such as watering troughs, swimming pools, streams, puddles, and cisterns. The adult worms are free-living, but the larvae are parasitic on arthropods, such as beetles, cockroaches, mantids, orthopterans, and crustaceans. About 351 freshwater species are known and a conservative estimate suggests that there may be about 2000 freshwater species worldwide. The name "Gordian" stems from the legendary Gordian knot. This relates to the fact that nematomorphs often tie themselves in knots.
Actinistia is a subclass of mostly fossil lobe-finned fishes. This subclass contains the coelacanths, including the two living species of coelacanths, both of the genus Latimeria: the West Indian Ocean coelacanth and the Indonesian coelacanth.
Geodia is a genus of sea sponge belonging to the family Geodiidae. It is the type genus of its taxonomic family.
Meconema thalassinum is an insect in the family Tettigoniidae known as the oak bush-cricket and drumming katydid. It is native to Europe, including the British Isles, and was introduced to the United States, first established in the west of Long Island and extending its range to Rhode Island and Scarsdale, Stony Brook, and Ithaca, New York.
The thorny-headed worm family Polymorphidae contains endoparasites which as adults feed mainly in fish and aquatic birds. When this taxon was erected by Meyer in 1931, a subfamily Polymorphinae was established in it. As the Polymorphidae as presently understood would then be monotypic, with no basal genera outside the Polymorphinae, the proposed subfamily is redundant for the time being and therefore most modern treatments simply omit it. Polymorphus minutus is an economically significant parasite in goose and duck farming.
The nematodes or roundworms constitute the phylum Nematoda, with plant-parasitic nematodes being known as eelworms. They are a diverse animal phylum inhabiting a broad range of environments. Taxonomically, they are classified along with insects and other moulting animals in the clade Ecdysozoa, and unlike flatworms, have tubular digestive systems with openings at both ends. Like tardigrades they have a reduced number of Hox genes, but as their sister phylum Nematomorpha has kept the ancestral protostome Hox genotype, it shows that the reduction has occurred within the nematode phylum.
Moniliformidae is a family of parasitic spiny-headed worms. It is the only family in the Moniliformida order and contains three genera: Australiformis containing a single species, Moniliformis containing eighteen species and Promoniliformis containing a single species. Genetic analysis have determined that the clade is monophyletic despite being distributed globally. These worms primarily parasitize mammals, including humans in the case of Moniliformis moniliformis, and occasionally birds by attaching themselves into the intestinal wall using their hook-covered proboscis. The intermediate hosts are mostly cockroaches. The distinguishing features of this order among archiacanthocephalans is the presence of a cylindrical proboscis with long rows of hooks with posteriorly directed roots and proboscis retractor muscles that pierce both the posterior and ventral end or just posterior end of the receptacle. Infestation with Monoliformida species can cause moniliformiasis, an intestinal condition characterized as causing lesions, intestinal distension, perforated ulcers, enteritis, gastritis, crypt hypertrophy, goblet cell hyperplasia, and blockages.
Oligacanthorhynchida is an order containing a single parasitic worm family, Oligacanthorhynchidae, that attach themselves to the intestinal wall of terrestrial vertebrates.
Centrorhynchidae is a family of parasitic worms. Three species of these thorny-headed worms in the genus Centrorhynchus were found to parasitize birds of prey and owls Slovakia. These hosts include Buteo buteo, Buteo rufinus, Falco tinnunculus, Asio otus, Strix aluco, Strix uralensis and Tyto alba.
Plagiorhynchidae is a family of parasitic Acanthocephalan worms.
Oroperipatus is a genus of Neotropical velvet worms in the family Peripatidae.
Gordius is a genus of worms in the phylum Nematomorpha, the horsehair worms. It was formerly treated as the only genus in the family Gordiidae, but the genus Acutogordius is now considered as distinct. The genus is distributed worldwide except for Antarctica, where no Nematomorpha have been recorded.
Paragordius varius is a parasite species in the horsehair worm group (Nematomorpha). They cycle between terrestrial and aquatic habitats and are most commonly known for their ability to manipulate their definitive host to jump into a pool of water, which allows them to complete their life cycle. Adults are over 10 cm long and 400 μm in diameter. P. varius is usually found in water or wet areas. The definitive hosts are mainly terrestrial arthropods, most often carabid beetles, crickets and praying mantids.
Tytthus is a genus of insects in family Miridae, the plant bugs. They are carnivorous, feeding upon the eggs of various planthoppers in the family Delphacidae, and thus are important in the biological control of pests. The genus is distributed throughout the Holarctic of the Northern Hemisphere, but species are also found in the tropics, in China, South America, Australia, and the Indo-Pacific.
Archotuba is a genus of elongated conical tubes that were seemingly deposited by colonial organisms. Known from the Chengjiang, its biological affinity is uncertain; it somewhat resembles the tubes of the 'priapulid' Selkirkia, but a cnidarian affinity is also possible. In the absence of soft parts, there really isn't enough data to confirm a biological affiliation.
Hystrichis is a genus of nematode worm with a spinose anterior end, resembling the introvert of priapulids. Species of Hystrichis live mainly in the digestive tract of aquatic birds.
Neoncicola is a genus of parasitic worms belonging to the family Oligacanthorhynchidae.
Nectonema is a genus of marine horsehair worms first described by Addison E. Verrill in 1879. It is the only genus in the family Nectonematidae described by Henry B. Ward in 1892, in the order Nectonematoidea, and in the class Nectonematoida. The genus contains five species; all species have a parasitic larval stage inhabiting crustacean hosts and a free-living adult stage that swims in open water.
Amorphinopsis is a genus of sea sponges belonging to the family Halichondriidae.
Gordioidea is an order of parasitic horsehair worms. Its taxonomy remains uncertain, but appears to be contained in the monotypic class Gordioida and contains about 320 known species.
