Mohsen Asgari, Seyedeh Najmeh Banihashemian, Sergio Álvarez-Ortega, Ali Eskandari
Summary A survey of nematodes in forested areas of northern Iran (Guilan Province) resulted in the description of a new species, Amphidelus andrassyi sp. nov. (Alaimida: Alaimidae), based on an integrative taxonomic approach combining detailed morphological, morphometric and molecular analyses. In addition, molecular data were obtained for an Iranian population of the known species Paramphidelus dolichurus . The new species belongs to the relatively long-bodied group of the genus Amphidelus , with adult females exceeding 3 mm in body length. Morphologically, it is most similar to A. acutus and A. longus and the distinguishing differences among these species are discussed in detail. Molecular analyses based on three 18S rRNA gene sequences provide reliable data for the genus Amphidelus and contribute to clarifying its phylogenetic placement within Alaimidae. Because complete sequences from other Amphidelus species are unavailable, molecular comparisons with congeners are limited. The molecular data obtained from Paramphidelus dolichurus are consistent with previous taxonomic hypotheses regarding its generic placement. Both species were recovered from decaying wood, highlighting the diversity of saproxylic nematodes in forest ecosystems of northern Iran. Beyond the description of a new species, the study also presents an updated taxonomic synthesis of Amphidelus , including an updated identification key to all valid species and a tabular morphometric compendium to facilitate species recognition and comparative studies. Overall, this study provides reliable molecular evidence contributing to a better understanding of phylogenetic relationships within the family Alaimidae.