''Pristionchus'' is a genus of

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

s (roundworms) in the family

Diplogastridae Diplogastridae, formerly Diplogasteridae, are a family of nematodes (roundworms) known from a wide range of habitats, often in commensal or parasitic associations with insects. Description Diplogastrid nematodes are characterized by a distinc ...

that currently includes more than 50 described species. They are known mainly as non-parasitic associates of insects, especially beetles, while others have been reported from soil, organic matter, or rotting wood. The genus includes '' P. pacificus'', a satellite model organism to the well-studied nematode ''

Caenorhabditis elegans ''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek ''caeno-'' (recent), ''rhabditis'' (ro ...

''.

Ecology and mouth dimorphism

In ''Pristionchus'' species associated with insects, the nematodes usually live on their hosts in a dormant stage (the dauer larva). After the death of the host insect, the nematodes resume development, feeding and reproducing on the decaying host carcass. Most species of ''Pristionchus'' show a

polyphenism A polyphenic trait is a trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions. It is therefore a special case of phenotypic plasticity. There are several types of polyphen ...

in their feeding structures, which allows the nematodes to access different food resources in this rapidly changing environment. In one form (the "stenostomatous" form), the mouth is elongated, narrow, and equipped with one small tooth, whereas in the other ("eurystomatous" form) it is short, wide, and with two large teeth. The emergence of a particular form depends on specific environmental conditions and the availability of food. Whereas the stenostomatous form feeds primarily on

microorganisms A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...