Background: Free-living nematodes of the Caenorhabditis spp., particularly Caenorhabditis elegans, are widely used as model organisms in studies of biological structures, such as soil ecology and evolutionary biology. Despite their importance, data on the diversity, distribution, and ecological occurrence of them in Iran remain scarce.


Objective: The present study aimed to identify genus Caenorhabditis and isolate the Iranian isolate of C. elegans using integrated morphological, culturing, and molecular approaches.


Methods: A total of free-living 570 nematodes were collected from five distinct climatic regions of Iran. Of which 150 specimens were selected for detailed morphomolecular analysis. Nematodes were isolated from each sample using the Baermann technique. Nine morphometric parameters were measured using a calibrated light microscope equipped with a digital camera. Nematodes were cultured on NGM medium enriched with Escherichia coli OP50. Molecular identification was performed using genus- and species-specific primers designed for the 28S rRNA gene locus of Caenorhabditis and C. elegans.


Results: Morphological analyses revealed nematodes belonging to five families, where teratocephalidae family was detected across most climatic regions, diplogastridae and cephalobidae showed the lowest frequency. The rhabditidae were isolated from temperate and humid, and cold and semi-arid climates. In this family, the mean body length and width were 645.58 µm and 30.58 µm, respectively. The first pharyngeal bulb was found as 32.23 µm across all regions. Length of the second pharyngeal bulb was 24.79 µm. Two specimens originating from temperate and humid weather produced a diagnostic 328-bp band specific to C. elegans, consistent with its morphological characteristics. Successful laboratory cultivation of Caenorhabditis specimens allowed observation of the complete life cycle (egg, larval, and adult stages).


Conclusion: This study provides the first confirmed evidence of C. elegans in Iranian ecosystems, specifically in temperate and humid regions of northern Iran, using morpho-molecular and culturing approaches. A considerable diversity of free-living nematodes belonging to the different families were identified. The detection of multiple families of free-living nematodes further highlights Iran as a suitable and diverse habitat for free-living nematode taxa, while the successful cultivation of Caenorhabditis paves the way for future ecological, evolutionary, and applied research in biomedical and veterinary sciences.