Rhabditida

Rhabditida is an order of nematodes in the phylum Nematoda, within the class Chromadorea. The group is highly diverse, containing numerous free-living species that inhabit soil and freshwater as well as several important parasitic lineages. Members of Rhabditida show a range of ecologies, from saprotrophic feeders on bacteria and fungi to obligate parasites of animals and insects.

A characteristic feature of many rhabditids is a rhabditiform esophagus, a distinctive deglutition apparatus that helps distinguish them from other nematode groups; however, morphological diversity is broad across the order, and precise identification often relies on a combination of morphology and molecular data. The order is subdivided into several subgroups and families, including the well-studied Rhabditidae, which contains the model organism Caenorhabditis elegans, widely used in biological research. Other notable rhabditids include lineages that form mutualistic associations with biocontrol-relevant bacteria.

Two prominent entomopathogenic lineages within Rhabditida are the families Heterorhabditidae and Steinernematidae. These nematodes parasitize insect larvae and rely on symbiotic bacteria (for example, Photorhabdus, Xenorhabdus) to help kill the host and release nutrients. Because of their ability to suppress pest insect populations, Steinernema and Heterorhabditis species are used in biological control programs.

Rhabditida is of importance to science and agriculture due to its inclusion of model organisms, its variety of ecological roles, and its application in pest management through entomopathogenic species.