This is the third part of a series of books dealing with the free-living nematodes of Hungary and also with the systematics of all the land-inhabiting nematodes. In the present volume the author discusses the second subclass of the class Penetrantia and its orders: Alaimida, Diphtherophorida, Mononchlida, Dorylaimida and the substance of Mermithida. From the order Alaimida 13 genera and 140 species, from the Diphtherophorida 8 genera and 154 species, from the Mononchida 45 genera and 454 species, from the Dorylaimida 263 genera and 2637 species, and finally, from the suborder Isolaimiina of Mermithida one genus and 12 species are presented or enumerated, respectively. That means this volume discusses a total of 330 valid genera and 3397 valid species.
All the families and genera or the mentioned orders are diagnosed and commented from taxonomical point of view. Since correct identification is vital in every field of nematology, the author provides keys to all families and genera. Genera containing species reported from Hungary are discussed in detail. World lists of their species and keys to their European representatives are added. The presentation of each species with recorded occurrence in Hungary is particularly throughout and detailed, and a good deal of them – at least one species of each genus – are illustrated. The author proposes a few new genera, several new combinations and some synonymizations.