Subclass Rhabditia is mostly composed of
parasitic
Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...
nematode
The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...
s (particularly in the
Strongylida
The Strongylida suborder includes many of the important nematodes found in the gastrointestinal tracts of ruminants, horses, and swine, as well as the lungworms of ruminants and the hookworms of dogs and cats.
Taxonomy
This suborder includes ( ...
), though there are some free-living species as well (particularly in the
Rhabditida
Rhabditida is an order of free-living, parasitic and microbivorous nematodes living in soil.
The Cephalobidae, Panagrolaimidae, Steinernematidae, and Strongyloididae seem to be closer to the Tylenchia, regardless of whether these are merg ...
).
Phasmids (posterior sensory structures) are well-developed, while
amphids (anterior sensory structures) are poorly developed or absent in this group.
In an alternate classification system, they are treated as
suborder
Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...
Rhabditina, with the orders listed here being ranked as
infraorder
Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between Family_(biology), family and Class_(biology), class. In biological classification, the order is a taxonomic rank used in the classific ...
s. Also, the
Diplogasterida
Diplogasterida was an order of nematodes. It was sometimes placed in a monotypic subclass Diplogasteria, but molecular phylogenetic evidence has shown it to be embedded in the family Rhabditidae (formerly Rhabditina). The confusion of having a h ...
, which are sometimes considered a
monotypic
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...
subclass, are probably better placed in the Rhabditia. On the other hand, the old placement of the
Ascaridida
Ascaridomorpha is an infraorder of parasitic roundworms in the order Rhabditida
Rhabditida is an order of free-living, parasitic and microbivorous nematodes living in soil.
The Cephalobidae, Panagrolaimidae, Steinernematidae, and Strongy ...
in Rhabditia instead of
Spiruria
Spirurina is a suborder of nematode worms in the order Rhabditida. Spirurina contains a diverse group of worms that inhabit soil, water, and other bodies of organism.
Footnotes
References