Rhabditid nematodes are very abundant in all types of soil and sediments of freshwater. They play important ecological roles mainly as primary consumers—their freeliving forms display saprophagous or bacteriophagous feeding habits—but also as animal parasites, in particular enthomopathogenic forms.
From a systematic point of view, rhabditids are a difficult nematode group whose classification has been muche discussed and whose diversity is far from being well known (Abolafia and Pena-Santiago, 2007).
|Anterior region of Cruznema tripartitum.|
|Rhabditid lip region, stoma and esophagus|
|Dauer larva; enduring survival stage; metabolically inactive; mouth closed; double cuticle.|
|Monovarial specimen showing spermatheca with sperm and distal end of reflexed ovary.|
|Spindle-shaped longitudinal muscle cells below the cuticle
and epidermis of a rhabditid nematode. The musculature is in four
strips, separated by the epidermal (hypodermal) chords. A process
extends from each cell to the dorsal or ventral nerve chord.
In Caenorhabditis elegans there are 24 mononucleate nerve cells in each subdorsal quadrant of the body, 24 in the right subventral quadrants and 23 in the left subventral quadrant. (Sulston and Horvitz, 1977; Waterston, 1988).
|Specimens from litter-soil interface, UC Davis campus. Photographs by H. Ferris.|
Under some conditions eggs are retained in the body of older females. The female dies, the eggs hatch, and juveniles feed on bacteria that are decomposing the maternal cadaver. The phenomenon has been termed "bagging" and "endotokia matricida". It has been variously interpreted as the result of diminished strength of the vaginal muscles that would be involved in allowing passage of the egg, and the resulting death of the worm (hence matricida), and also as a facultative vivipary, survival adaptation that provides resources for the juveniles (Chen and Caswell-Chen, 2004).
|Bagging or Endotokia Matricida: Juveniles
beginning to emerge from the depleted maternal cadaver of a rhabditid
Photograph by Jonathan Nivens
Most soil Rhabditidae are considered to be bacterial-feeding r-strategists that respond rapidly to environmental enrichment and increase in bacterial biomass.
Other species are parasites of invertebrates or have commensal relationships with insects (Morand et al., 2004).
Several different genera are associated with molluscs, including Rhabditis, Caenorhabditis and Phasmarhabditis. (e.g. Agfidae and Angiostomatidae), Phasmarhabditis spp. are facultative parasites that live on compost, leaf litter, slug faeces, and dead earthworms and insects. Some have a necromenic strategy in relation to the larger slug species. Caenorhabditis elegans can invade the intestine of molluscs and exit with feces. Phasmarhabditis hermaphrodita has been developed as a commercial biological control agent of slugs and snails (Pieterse et al., 2017).
, 39:263-274.herty, 1953 and Diploscapter Cobb, 1913, with Description of P. spiculocrestata sp. n. and a Species Protorhabditis Key.
Chen, J, Caswell-Chen, E.P. 2004. Facultative vivipary is a life-history trait in Caenorhabditis elegans. J. Nematology 36:107-113.
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Pieterse, A., Malan, A.P., Ross, J.L. 2017. Nematodes that associate with terrestrial molluscs as definitive hosts, including (Rhabditida: Rhabditidae) and its development as a biological molluscicide. J. Helminthol. 91:517-527.
Sulston, J.E. and H.R. Horvitz. 1977. Post-embryonic cell lineages of the nematode Caenorhabditis elegans. Developmental Biology 56:78:577-597.
Waterston, R.H. 1988. Muscle. Pp 281-335 in W.B. Wood (ed). The Nematode Caenorhabditis elegans. Cold Spring Harbor Laboratory.
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