Desmodoridae Filipjex, 1922
A family of free-living marine nematodes.
The family Desmodoridae has a large number of species, of which very few have been described. Ecological studies on marine nematodes record nematodes of the Desmodoridae in deep-sea sediments, usually in low numbers, with their relative abundance reaching a maximum of 1% of the total mass (Soetaert and Heip, 1995).
The deep sea is the largest, the least known and one of the least studied environments on the planet. It contains extremely large habitats, and millions of square kilometers of continental slopes and abyssal plains. Frequently, more than 90% of the species collected in a typical abyssal sediment sample are new to science. The species richness of such assemblages often exceeds expectations. Because of the diversity and abundance, it is difficult to select enough specimens of the same species for species descriptions:. Although there may be several hundred unknown species in a single sample of 1000 nematodes, most of the species present may be represented by only one or a few specimens (Moura et al., 2014).
Desmodorella sp (family Desmodoridae)
Head end with spiral amphid and hair-like setae
(from Cesaroni et al., 2017)
Six Subfamilies: Desmodorinae, Spiriniinae, Stilbonematinae, Pseudonchinae, Molgolaiminae and Prodesmodorinae
Subfamily Desmodorinae Filipjev, 1922:
Subfamily Spiriniinae Chitwood, 1936:
cuticle finely or sometimes coarsely striated.
head not demarcated as a cephalic capsule.
amphideal fovea a simple spiral, usually located far anterior on the body.
buccal cavity rather small, from minute to medium-sized, with a distinct or a minute dorsal tooth; two smaller ventro-sublateral teeth present or absent, or there may be 3 teeth of the same size.
adhesion tubes or ambulatory setae absent.
gubernaculum without dorsal apophyses.
Vulva usually posterior to middle of body.
Ref: Cavalcanti et al., 2009; Leduc and Zhao, 2016.
Subfamily Stilbonematinae Chitwood, 1936:
Body filiform, very long, up to 10mm, sometimes enlarged anteriorly
Cuticle unifromly annulated, no lateral fields or ornamentation
Stoma minute, buccal cavity very small or absent
Pharynx short, divided into procorpus, slender isthmus and posterior bulb
Cuticle often densely covered with ectosymbiotic chemoautotrophic bacteria embedded in a film of slime
Usually inhabit sheltered intertidal sediments.
Subfamily Prodesmodorinae Lorenzen, 1981
Cuticle with faint but distinct straition
Head slightly offset
Anterior sensilla in 6+6+4 (inner and outer labial and cephalic) configuration
Amphidial fovea round to oval, posterior to buccal cavity
Short somatic setae throughout body surface
Buccal cavity slender with minute teeth
Pharyngeal bulb with internal cuticular lining of pharyngeal lumen
Females amphidelphic, ovaries reflexed
Males usually rare, monorchic, spicules short, arcuate; gubernaculum present.
Tailconical with terminal spinneret.
Type genus: Prodesmodora Micoletzky, 1923
Leduc and Zhae 2016 propose that this subfamily be removed from the Desmodoridae because it includes terrestrial and freshwater nematodes.
Subfamily Molgolaiminae: Jensen, 1978
Short nematodes, usually <1mm long
Cuticle appears smooth to finely striated
Head narrow, inner and outer labial semsilla reduced, very small; cephalic setae small but distinct
Amphid fovea rounded, some distance posterior to cephalic setae
Buccal cavity narrow, weakly sclerotized, small teeth
Posterior pharyngeal bulb withinner cuticular lining
Females amphidlephic. ovaries reflwexed.
Male monorchic; spicules and gubernaculunm varied in seze and shape
Type genus Molgolaimus Ditlevsen, 1921
Subfamily Pseudonchinae: Gerlach & Riemann, 1973
Cuticle finely striated
Buccal cavity large, tubular, without teeth but rows of denticles at anterior margin
Subcephalic setae present
Amphid fovea as single lops or round cryptospirals
Cuticle with thin midventral alae
Type genus Pseudonchus Cobb, 1920
An interesting feature of the family Desmodoridae is the sexual dimorphism of the amphids. In some species the amphid shape may extend longitudinally in males while in females it is a spiral.. Sexual dimorphism of amphids has been observed in several genera of marine Desmodoridae, including Onyx Cobb, 1891; Pseudochromadora Daday, 1899; Chromaspirina Filipjev, 1918; Croconema Cobb, 1920; Leptonemella Cobb, 1920; Zalonema Cobb, 1922; Spirinia Gerlach, 1963; Echinodesmodora Blome, 1982; and Psammonema Verschelde & Vincx, 1995 (Moura et al., 2014).
Cavalcanti, M.D.F., Da Silva, M.C., Da Fonseca-Genevois, 2009. Spirodesma magdae nov. gen. nov. sp. (Nematoda: Desmodoridae) from the Brazilian deep sea (Campos Basin, Rio de Janeiro, Brazil). Zootaxa 2096: 109–118.
Cesaroni, L. Guidi, L., Balsamo, M., Semprucci, F. 2017. Scanning electron microscopy in the taxonomical study of free-living marine nematodes. Microscopie 28:6970
Leduc, D., Zhao, Z. 2016. Phylogenetic relationships within the superfamily Desmodoroidea (Nematoda: Desmodorida), with descriptions of two new and one known species. Zoological Journal of the Linnean Society, 176: 511–536. https://doi.org/10.1111/zoj.12324
Moura, J.D.R., Da Silva, M.C., Esteves, A.M. 2014. Four new species of Desmodora (Nematoda) from the deep south-east Atlantic, and a case of intersexuality in Desmodoridae. J. Mar. Biol. Associ. UK. 94:85-104.
Soetaert, K. and Heip, C.H.R. 1995. Nematode Assemblages of Deep-Sea and Shelf Break Sites in the North-Atlantic and Mediterranean-Sea. Marine Ecol. Progress Series 125:171-183.
Tchesunov. A.V. 2013. 7.13 Order Desmodorida de Coninck, 1965 In Schmidt-Rheas and de Gruyter, W. Handbook of Zoology.Gastrocticha, Cycloneuralia, Gnatifera. Volume 2: Nematoda
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