Revised 08/20/26
Phylum Nematoda
Class Chromadorea
Subclass Chromadoria
Order Chromadorida
Suborder Chromadorina
Superfamily Chromadoroidea
Selachinematidae Cobb, 1915
A family of marine nematodes.
Females: didelphic-amphidelphic, ovaries reflexed
Males: Usually two outstretched testes, either on same or different sides of the intestine; pre-cloacal supplements usually present, usually cup-shaped, sometimes setose, papilliform, rarely tubular.
Species of Selachinematidae are specialized predators feeding on other nematodes, or at least on other large-sized items. Ingestion of prey nematodes by selachinematid species has been documented (Allgen, 1939; Jensen, 1987; Okhlopkov, 2003).
Usually, the quota of predatory nematode species is higher in coarse-grained sediments and thus the role of selachinematids as regulators of community structure may be more significant in in sandy sediments (Warwick, 1971; Kennedy, 1994)
Two subfamilies: Choniolaiminae Schuurmans-Stekhoven & Adam, 1931 and Selachinematinae Cobb, 1915
Choniolaiminae: Buccal cavity spacious, divided into two compartments, anterior portion broad, posterior narrow; reinforced by cuticularised rhabdions in both portions. Mandibles absent.
Selachinematinae: Buccal cavity spacious, divided into two compartments, with posterior rhabdions modified into protrusible denticulate mandibles
Family Characteristics:
Marine nematodes, considered voracius predators.of, among others, smaller nematodes.
Most often reported from relatively coarse sediments in shallow water environments but also occur in deep-sea habitats.
Usually a stout cylindrical body, anteriorly truncate.
Cuticle punctated with or without lateral differentiation.
Head sensillae may be jointed.
Multispiral amphids.
Buccal cavity spacious, divided into two compartments, Complex buccal armament of rhabdions, denticles, or heavy mandibles, for capture of nematode prey.
Pharynx wide and strongly muscular, often with anterior and posterior muscular thickenings.with or without posterior bulb, anterior bulb sometimes present
Percentages of selachinematids and other predator taxa in nematode assemblages are usually low in mud and silty sediments., more abundant in sandy sediments with higher species diversity and prey density.
12 genera as of 2016.
Halichoanolaimus the most common, diverse and widely distributed; Cheironchus less common but widely distributed.
Ref: Leduc, 2013; Leduc and Zhao, 2016; Tchesunov, 2013; Tchesunov et al., 2020.
Predatory and omnivorous nematodes have been observed to dominate the nematode species abundance in sandy sediments. In a study of beaches of the East China Sea, predaceous nematodes dominated the meiofaunal assemblages contributing to about 62% of the total meiofaunal abundance. Of these nematodes, Thoracostomopsidae were the most predominant and amounted to more than 60% of the nematode abundance while species of the Selchinematidae contributed about 5 % of total nematode abundance. Members of the Thoracostomopsidae and the Selachinematidae are large nematode sand there may be a significance to the porosity of coarse sandy habitats in the abundance of predators of these families (Shi & Xu 2016; 2017). A reasonable assumption is that nematodes of the Thoracostomopsidae and the Selachinematidae play key roles in regulating the micro- and meiobenthic communities of sandy beach environments.
Allgen, C.A. 1939. Räuberische Ernährungsweise mariner Nematoden, insbesondere Halichoanolaimini. Folia Zoologica et Hydrobiologica 9, 321-32
Bongers, T. De Nematoden van Nederland.
Goodey, T and J.B. Goodey, 1963. Soil and Freshwater Nematodes. Methuen. London
Jensen, P. 1987. Feeding ecology of free-living aquatic nematodes. Marine Ecology Progress Series 35, 187-196.
Kennedy, A.D. 1`994.. Predation within meiofaunal commnities: description and results of a rapid-freezing method of investigation. Marine Ecology Progress Series 114, 71-79.
Leduc, D. 2013. Two new genera and five new species of Selachinematidae (Nematoda, Chromadorida) from the continental slope of New Zealand. European Journal of Taxonomy 63: 1-32.
Leduc, D., Zhao, Z.Q. 2016. Molecular characterisation of five nematode species (Chromadorida, Selachinematidae) from shelf and upper slope sediments off New Zealand, with description of three new species. Zootaxa 4132:59-76.
Neira, C., Decraemer, W. 2009. Desmotersia levinae, a new genus and new species of free-living nematode from bathyal oxygen minimum zone sediments off Callao, Peru, with discussion on the classification of the genus Richtersia (Chromadorida: Selachinematidae. Organisms, Diversity and Evo;ution 9, 1:e1-1.e15
Okhlopkov, J.R. 2003. [Feeding of free-living nematodes of the families Selachinematidae and Richtersiidae in the White Sea.] Proceedings of the Pertsov White Sea Biological Station 9, 127-139.
Shi, B. and Xu, K. 2016. Four new species of Epacanthion Wieser, 1953 (Nematoda: Thoracostomopsidae) in intertidal sediments of the Nanji Islands from the East China Sea. Zootaxa 4085 (4): 557-574.
Shi, B.Z., and K.D. Xu. 2018. Two new rapacious nematodes from intertidal sediments, Gammanema magnum sp. nov. and Synonchium caudatubatum sp. nov. (Nematoda, Selachinematidae). European Journal of Taxonomy 405: 1-17.
Tchesunov, A.V. 2013. 7.12 Order Chromadorida Chitwood, 1933. In Schmidt-Rheas and de Gruyter, W. Handbook of Zoology.Gastrocticha, Cycloneuralia, Gnatifera. Volume 2: Nematoda
Tchesunov, A., Jeong, R. Lee W. 2020. Two New Marine Free-Living Nematodes from Jeju Island Together with a Review of the Genus Gammanema Cobb 1920 (Nematoda, Chromadorida, Selachinematidae). Diversity 2020, 12, 19; doi:10.3390/d12010019.
Warwick, R.M. 1971. Nematode associations in the Exe estuary. Journal of the Marine Biological Association of the United Kingdom 51, 439-454
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