Species inquirendum.
The specimen encountered in my samples mostly resemble the description of Sigmophoranema rufum in Free living Marine Nematodes (Part II) by H.M. Platt and R.M. Warwick and the description in Gerlach, S. A. (1951). Revision der Metachromadoracea, einer Gruppe freilebender mariner Nematoden. Kieler Meeresforsch. 8 (1): 59-75 (Sigmophora rufum)
In Armenteros et. al. 2014, Revision of Desmodorinae and Spiriniinae (Nematoda: Desmodoridae) with redescription of eight known species, European Journal of Taxonomy 96: 1-32, this taxon is classified as taxon inquirendum because of the poor description of the type specimen. Also the genus Sigmophoranema is classified as a synonym of Onyx. The valid Sigmophoranema species were transfered to Onyx, but not S. rufum.
For now, i refer to these specimen as Sigmophoranema rufum.