Thirteen specimens of Microtus levis were collected from Golestan province, northeast Iran. The specimens were studied based on their external characters, skull and dental morphology, and specially karyology. Specimens of M. levis from the northeast of Iran were also compared with other species of the arvalis group from Iran and specimens of M. levis from Turkey. The specimens demonstrated that 2n ¼ 54 and fundamental number FN¼ 54. The karyological results were similar between specimens from northeast Iran and those from Turkey, but they were different from specimens of Europe. In addition, the morphometric characters of M. levis, including head and body length (mean ¼ 105.77_ 7.53), length of condylobasal (mean ¼ 24.96_ 0.97), length of bullae (mean ¼ 6.57 _ 0.34), and dental characters consisting of maxillary tooth row (mean ¼ 6.17 _ 0.25) and mandibular tooth row (mean ¼ 5.60 _ 0.33), were different from those of other species of the arvalis group.

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