Monotypic protostome genera

Titaniloricus is a genus of small marine animal in the phylum Loricifera. It contains a single species, Titaniloricus inexpectatovus, described by Gunnar Gad in 2005. It has been collected from the abyssal plain in Angolan waters of the Atlantic Ocean.

Paucidentula is a monotypic genus of worms belonging to the monotypic family Paucidentulidae. The only species is Paucidentula anonyma.

Rastrognathia is a monotypic genus of worms belonging to the monotypic family Rastrognathiidae. The only species is Rastrognathia macrostoma.

Problognathia is a monotypic genus of worms belonging to the monotypic family Problognathiidae. The only species is Problognathia minima, also known as the problematic jaw worm.

Australoricus oculatus is a species of Loricifera, a species of microscopic marine sediment-dwelling animals, in the family Nanaloricidae. It is the only described species in the genus Australoricus. It was discovered in sea caves off New South Wales in Australia.

Golvanacanthus is a monotypic genus of acanthocephalans (thorny-headed or spiny-headed parasitic worms) containing a single species, Golvanacanthus blennii, that infests animals.

Heptamegacanthus is a genus of acanthocephalans (thorny-headed or spiny-headed parasitic worms) containing a single species, Heptamegacanthus niekerki, that is a parasite of the endangered giant golden mole. It is found only in isolated forests in the Transkei and near East London, both in South Africa. The worms are about 4 mm long and 2 mm wide with minimal sexual dimorphism. An individual's body consists of a short, wide trunk and a tubular feeding and sucking organ called the proboscis which is covered with hooks. The hooks are used to pierce and hold the rectal wall of its host.

left|thumb|Life restoration Paucipodia inermis is a lobopod known from the Lower Cambrian Chengjiang lagerstätte.

Pelmatosphaera is a monotypic genus of worms belonging to the monotypic family Pelmatosphaeridae. The only species is Pelmatosphaera polycirri.

Australiformis is a monotypic genus of acanthocephalans (thorny-headed or spiny-headed parasitic worms) containing a single species, Australiformis semoni, that infests marsupials in Australia and New Guinea. Its body consists of a proboscis armed with hooks which it uses to pierce and hold the gut wall of its host, and a long trunk. This genus resembles species in the genus Moniliformis but is characterized by a lack of spiral muscles in the outer wall of the proboscis receptacle. The proboscis is armed with 12 rows of 13 to 15 hooks which are used to attach themselves to the small or large i