LAUSR

Abstract Aulolaimus is an old and, still nowadays, enigmatic nematode taxon. The aim of this contribution is to explain and discuss the morphological pattern of Aulolaimus in the light of new evidence and to set the basis to elucidate its taxonomy and systematics. The close relationship of Aulolaimus with Isolaimium, traditionally located in the questionable order Isolaimiida, is demonstrated with morphological and molecular analyses, constituting a separate group from other nematode orders and closely related to the araeolaimid genus Cylindrolaimus. According to this, the order Isolaimiida is considered valid and Aulolaimus and other genera belonging to the family Aulolaimidae are transferred to this order. A list of species of Aulolaimus and a key for their identification are included. Aulolaimus agricola sp. n. and Aulolaimus forestalis sp. n. are proposed from specimens previously described from Iran.