Robbea		Contents		Rev: 03/26/2025
		Classification		Biology and Ecology
		Morphology and Anatomy		Life Cycle
Return to Robbea Menu				Ecosystem Functions and Services
		Distribution		Management
Return to Desmodoridae Menu		Feeding		References
		Go to Nemaplex Main Menu		Go to Dictionary of Terminology

Classification:

Chromadorea

  Chromadoria

   Desmodorida

Desmodorina

             Deamodoroidea

                Desmodoridae

       Stilbonematinae

        Robbea Gerlach, 1956

     

Type species of the genus: Robbea caelestis Gerlach, 1956

    Synonyms:
     

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Morphology and Anatomy:

Species of Robbea are difficult to distinguish using single morphological characters. Scharhauser et al., 2025 used a principal component analysis (PCA), based on 14 morphological characters, to separate the species from each other.

• Stilbonematinae; body long (L = 2.8-8.3 mm), slender (a > 110), cuticle thin, transverse striation extremely fine,
• Cephalic capsule with block layer, creating a honey-comb structure in surface view;

• Head capsule with thickened cuticle,

• Sensilla in 6-6-4 pattern, papilliform and setiform, first circle of finger-like papillae retracted into mouth opening, second as six conical papillae at margin of buccal membrane, third as four long cephalic setae directed anteriorly, close to the anterior margin of the amphidial fovea;

•  Somatic setae minute or absent, except for subventral rows of papilliform setae on the male tail, instead eight rows of cuticular pores corresponding to the GSOs; .
• Glandular sense organs (GSOs) dark-purple color in live animals only. GSOs in eight rows, two sublateral rows on each side and two submedian rows dorsally and ventrally, respectively
• Amphidial fovea flat with shallow spiral groove, ventrally wound.
• Pharynx with swollen muscular corpus, set off from the long and thin isthmus, small mainly glandular terminal bulb. .
• Tail conical
• Body diameter decreases at onset of bacterial coat,  Bacteria arranged with their longer axis parallel to the nematode�s cuticle

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Distribution:

Marine nematodes in tidal sands and coral reefs.

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Feeding:

Nematodes in the subfamily Stilbonematinae of the Desmodoridae are associated with, and feed on,  dense coatings of sulfur-oxidizing chemoautotrophic gammaproteobacteria with which they are apparently obligately symbiotic. The nematodes feed on the bacterial symbionts.

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Biology and Ecology:

Fe-Br inclusions occur inside the the glandular sense organs (GSO's).  So far (2025), Fe-Br inclusions have only been found in the genus Robbea. The GSOs connect to the exterior of the nematode body via hollow setae. The symbiotic associations between bacteria and nematodes are species-specific couplings that are initiated and maintained by secretions of the neurosecretory cells of the GSOs  (Bulgheresi et al., 2006; Scharhauser et al., 2025).

The nematodes migrate through the chemocline in the sediments of the intertidal zone to provide their ectosymbionts with both oxygen and sulfide. Essentially, the nematodes farm their bacterial associates by migrating to ocean sediments rich in hydrogen sulfide (Bulgheresi Reference Bulgheresi2011; Murfin et al. Reference Murfin, Dillman, Foster, Bulgheresi, Slatko, Sternberg and Goodrich-Blair2012).. The chemoautotrophic gammaproteobacteria derive energy by oxidizing sulfides.  In turn, the nematodes feed on the bacterial symbionts as their source of nutrients and energy (Ott and Novak 1989, Ott et al. 1991; Scharhauser et al., 2025).

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Life Cycle:

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Ecosystem Functions and Services:

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Management:

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References:

Armenteros, M., Ruiz-Abierno, A., Decraemer, W. 2014. Taxonomy of Stilbonematinae (Nematoda: Desmodoridae): description of two new and three known species and phylogenetic relationships within the family. Zool; J. of the Linnean Soc. 171-1-21.

Bulgheresi S, Schabussova I, Chen T et al. 2006. A new C-type lectin similar to the human immunoreceptor DC-SIGN mediates symbiont acquisition by a marine nematode. Applied and Environmental Microbiology 72:2950-2956. https://doi.org/10.1128/AEM.72.4.2950-2956. 2006

Bulgheresi, S. 2011. Calling the roll on Laxus oneistus immune defense molecules. Symbiosis 55, 127-135.

Chitwood, B.G. 1936. Some marine nematodes from North Carolina. Proc. Helmint. Soc. Wash. 3: 1-16.

Gerlach S.A. 1956. Die Nematodenbesiedlung des tropischen Brandungsstrandes von Pernambuco: Brasilianische Meeres-Nematoden, II. Kieler Meeresforschungen 12:202-218.

Murfin, K. E., Dillman, A. R., Foster, J. M., Bulgheresi, S., Slatko, B. E., Sternberg, P. W. and Goodrich-Blair, H. 2012. Nematode-bacterium symbioses - cooperation and conflict revealed in the omics  age. Biological Bulletin 223, 85-102.

Ott, J, Novak R. 1989. Living at an interface: meiofauna at the oxygen/sulfide boundary of marine sediments. In: Tyler PA (ed.), In Reproduction, Genetics and Distribution of Marine Organisms. Fredenborg: Olsen & Olsen, 415-422.

Ott, J.A., Novak R,, Schiemer, F. et al. 1991. Tackling the sulfde gradient: a novel strategy involving marine nematodes and chemoautotrophic ectosymbionts. Marine Ecology 12:261-279. htps://doi. org/10.1111/j.1439-0485.1991.tb00258.x

Scharhauser, F. et al. 2025.  Revision of the genus Robbea (Stilbonematinae: Desmodoridae), worldwide abundant marine nematodes with chromophoric Fe-Br inclusions and the description of a new stilbonematine genus, Zoological Journal of the Linnean Society, 203, Issue 1, January 2025, zlae005, https://doi.org/10.1093/zoolinnean/zlae005

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Copyright © 1999 by Howard Ferris.
Revised: March 26, 2025.