Family Rhabditidae

                                 Rev 02/26/2024



          Rhabditidae Oerly, 1880

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). They are mainly distinguished by their lip characteristics and shape of appendages, male tail characters, especially the number and arrangement of genital papillae, presence/absence and shape of bursa, shape of spicule and gubernaculum, and female/hermaphrodite tail morphology (Sudhaus, 2011; Scholze & Sudhaus, 2011). Phylogenetically, the family is not monophyletic; other families and non-Rhabditidae clades, e.g., strongyloidids, are located between two independent ‘Rhabditidae’ groups of genera groups (e.g., van Megen et al., 2009; Smythe et al., 2019).


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.  

Morphology and Anatomy:


Generalized Characteristics of anterior and posterior regions of Rhabditidae (from Sudhaus and Fitch, 2001)



Basic  Body Plan of Nematodes in the Family Rhabditidae ( from Sudhaus, 2014)

(1) Adults about 1  mm long; females slightly longer than males on average.

(2) Six lips with sensilla in two concentric circles around the mouth opening; small amphid pores at the base of the lateral lips; lateral deirids encircling the isthmus posterior to the nerve ring; lateral postdeirids located in the posterior half of the body.

(3) Stoma tube-like with prismatic cross section; a short cheilostom in the lip region, a gymnostom of half the stoma length, a stegostom enveloped by a sleeve of pharyngeal tissue forming; stoma terminating in a glottoid apparatus bearing cuticular structures like denticles.

(4) Pharynx tripartite, muscular with a corpus (with anterior radial tubes for reflux of water during the filtering of bacteria), a narrower cylindrical isthmus and a terminal bulb with three rhabditoid valves (the grinder) to crush bacteria, followed by two cuticularized chambers (double haustrulum) and a funnel-like cardia opening to the intestine.

 (5) Secretory-excretory system H-shaped with an osmoregulation function and, at least in the dauerlarva, shows pulsations of a tiny ampulla at the beginning of the duct.

(6) Females with a midbody vulva with a circular opening and two opposed (amphidelphic) genital branches, which are homodromously (within the growth zone of the ovaries) reflexed to the dorsal, the anterior branch right of intestine, the posterior branch on the left side.

(7) Tails of juveniles, and probably also tail of the female, conical tapering.

(8) Males monorchic; testis to the right of intestine and ventrally reflexed.

(9) Posterior end of the male with a series of nine bilateral pairs of sensitive genital papillae subventrally, presumably three of them anterior of the cloaca, and two postcloacal papillae (in positions five and seven) oriiented more sublaterally/dorsally. The similar arrangement of papillae (including the position of the first papilla far anterior of the cloaca) is considered symplesiomorphic.

(10) A pair of phasmids posterior of genital papillae with a ventral opening and circumcloacal sensilla consisting of one on the precloacal lip and a pair postcloacally.

(11) Copulation involves the male to curl its posterior end around the female body; often a small gelatinous copulatory plug is deposited to seal the vulva. Spicules separate and gubernaculum unforked.

(12) Life cycle includes an ecologically important dauerlarva, a developmental alternative to the normal third-stage juvenile, which, by retaining the cuticle of the preceding juvenile stage and living from intestinal reserves, can withstand periods of unfavorable conditions.

(13) Gonochoristic reproduction, presumably longliving and oviparous, steadily producing eggs over a longer period..


Life Cycle:

 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; Seurat, 1914).

Bagging or Endotokia Matricida:  Juveniles beginning to emerge from the depleted maternal cadaver of a rhabditid nematode
Photograph by Jonathan Nivens

Copulation in the Rhabditidae:

Various copulatory positions can be distinguished in nematodes. The most common form is the  “spiral form” or “radial form” in which the male winds  the posterior portion of its body spirally around, and perpendicular to, the body axis of the female. The stability of the male in this form of copulation by ventromedian supplements that are precloacal. With the evolution of the bursa, as, for example, in the Rhabditidae, the “parallel form” of copulatory position became possible; males could be stabilized on the surface of the female’s body with the aid of a “suction-cup-like” bursa and supported by the secretion of cloacal glands.

The position of the female vulva does not appear to influence the form of copulation; howvere, it would seem that the spiral form of copulation would be difficult if the vulva is very posterior in position. The evolution of the bursa and the arrangement of the bursal papillae must be of considreble importance in copulatory behavior. Although the primary function of the bursal papillae is sensory, they also allow the formation and support of a broad bursal velum whic facilitates grasping and orientation on the female body in the parallel form of copulation.

The shape and size of spicules must also be adapted to the copulatory position.  In the spiral form with the absence of a bursa, curved spicules should provide an advantage in penetration of the vulva.  On the other hand, in parallel copulation as in most Rhabditidae, straighter and longer  spiculse are probably an advantage.

In rhabditid species with a closed bursa, the suction effect between the busra and female body is optimized by secretion of copulatory cement from the caudal glands.  When copulation isds completed, the cement remains covering the vulva as a copulatory plug which may remain in place until egg production commences (Sudhaus and Fitch, 2001)



Most soil Rhabditidae are considered to be bacterial-feeding r-strategists that respond rapidly to environmental enrichment and increase in bacterial biomass.  Bacteria are ingested  in the soil solution; the pharyngeal corpus has anterior radial tubes for reflux of water during the filtering of bacteria and a terminal bulb with three rhabditoid valves (the grinder) to crush ingested bacteria (Sudhaus, 2014).

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.  Unlike true mollusc parasites (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).



Abolafia, J and Pena-Santiago, R. 2007. Nematodes of the Order Rhabditida from Andalucía Oriental, Spain. The Genera Protorhabditis (Osche, 1952) Dougherty, 1953 and Diploscapter Cobb, 1913, with Description of P. spiculocrestata sp. n. and a Species Protorhabditis Key. y, 39:263-274.

Chen, J, Caswell-Chen, E.P. 2004. Facultative vivipary is a life-history trait in Caenorhabditis elegans. J. Nematology 36:107-113.

MorandS.WilsonM.J. & GlenD.M. (2004Nematodes (Nematoda) parasitic in terrestrial gastropods. pp. 525557 in BarkerG.M. (Ed.Natural enemies of terrestrial molluscsWallingfordCABI Publishing.

Pieterse, A., Malan, A.P., Ross, J.L. 2017. Nematodes that associate with terrestrial molluscs as definitive hosts, including Phasmarhabditis hermaphrodita (Rhabditida: Rhabditidae) and its development as a biological molluscicide. J. Helminthol. 91:517-527.

Scholze, V.S. & Sudhaus, W. 2011.. A pictorial key to current genus groups of “Rhabditidae”. Journal of Nematode Morphology and Systematics 14: 105-112.

Seurat, L.G. 1914. Sur un cas d’endotokie matricide chez un oxyure. Comptes-Rendues de la Société de Biologie 76:850-853.

Smythe, A.B., Holovachov, O. & Kocot, K.M. 2019.. Improved phylogenomic sampling of free-living nematodes enhances resolution of higher-level nematode phylogeny. BMC Evolutionary Biology 19, 121: DOI: 10.1186/s12862-019-1444-x

Sudhaus, W. (2011). Phylogenetic systematisation and catalogue of paraphyletic “Rhabditidae” (Secernentea, Nematoda). Journal of Nematode Morphology and Systematics 14, 113-178.

Sudhaus, W. 2014. 7.17 Order Rhabditina: "Rhabditidae".  In: A. Schmidt-Rhaesa (ed.): Handbook of Zoology. Gastrotricha, Cycloneuralia and Gnathifera, Vol. 2: Nematoda. W. deGruyter, Berlin, Boston: 537–555.

Sudhaus, W. and Fitch, D. 2001. Comparative studies on the phylogeny and systematics of the Rhabditidae (Nematoda). J. Nematology 33:1-70.

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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