Rev 03/14/2023

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Thonus Thorne, 1974

Note: Although Thonus is considered a synonym of Crassolobium and, based on dates of publication, would be the junior synonym, Pena-Santiago and Ciobanu (2007) suggest a reversal of the precedence condition because (i):the name Thonus identifies a highly diversified taxon (more than 40 species are currently named with this generic substantive while Crassolabium is a poorly known and seldom used name, with only two species; (ii) Thonus is a name that identifies a worldwide-distributed taxon, recorded in many (50) bibliographic references on taxonomical, faunistical and ecological subjects, whereas by contrast only a few (10) references are available on Crassolabium, mostly discussing its taxonomy and status; (iii) Thonus is a name that identifies a rather well-defined morphological pattern among dorylaimid nematodes, and relevant morphological (and also biogeographical and ecological information) is associated with it, obviously, that is not at all the case of Crassolabium; (iv) the etymology of Crassolabium, meaning thick or fat lip, refers to a peculiar morphological feature that does not fit the Thonus pattern and whose taxonomical value has been demonstrated to be of minor significance and interest.

However, despite those arguments, Pena-Santiago and Alvarez-Ortega (2014) listed Thonus as a junior synonym of Crassolobium!  In the same paper, the rounded tail members of the subfamily Qudsianematinae of the family Qudsianematidae were transferred to a new subfamily (Labronematinae) of the family Dorylaimidae.  In his recent book, Dorylaimida Mundi (Nematoda) 2021, Pena-Santiago, ever and appropriately an advocate for the Rules of Zoological Nomenclature, listed the current species of Thonus under the genus name Crassolobium.


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  Designated omnivore-predator by Yeates et al (1993).     

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Pena-Santiago, R. and Ciobanu, M. 2007. On the Identity of the Genus Crassolabium Yeates, 1967 (Dorylaimida: Qudsianematidae). J. Nematology 39:231-236.

Pena-Santiago, R. and S. Alvarez-Ortega. 2014. An integrative approach to assess the phylogeny and the systematics of rounded-tailed genera of the subfamily Qudsianematinae (Nematoda, Dorylaimida). Zoologica Scripta 43:418-428.

Yeates, G.W., T. Bongers, R. G. M. De Goede, D. W. Freckman, and S. S. Georgieva. 1993. Feeding habits in soil nematode families and genera—An outline for soil ecologists. Journal of Nematology 25:315-331.

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Copyright © 1999 by Howard Ferris.
Revised: March 14, 2023.