New insights into the evolutionary relationships of Opisthodorylaimus sylphoides (Williams, 1959), with proposal of Sylphodorylaimus n. gen. (Nematoda, Dorylaimida, Thornenematidae)

A new nematode genus, Sylphodorylaimus n. gen., is proposed to accommodate one species previously classified under Opisthodorylaimus Ahmad & Jairajpuri, 1982. The study of two Iranian populations of O. sylphoides (Williams, 1959), collected in natural areas, including their morphological, morphometrical and molecular (28S rDNA) characterisation, revealed that females were almost identical to those of other known population, but also that their males, found and described for the first time, displayed long and filiform tail, similar to that observed in females. Since Opisthodorylaimus is characterized by showing a conspicuous sexual dimorphism in tail shape, with males having short and rounded tail, O. sylphoides must not be retained under this genus. The new taxon is compared with and separated from other genera of Thornenematidae Siddiqi, 1969, and its evolutionary relationships are discussed.