Eight extant species have been so far recognized for Calomyscus Thomas, 1905 which is distributed in the west of Asia. The only species which was reported from the Zagros Mountains in western and southern Iran was C. bailwardi. However, based on the integrative methods such as molecular, morphometric and karyological studies a new species is worth to be described other than C. bailwardi from the Zagros Mountains. In the present survey a new species which has been distributed in western regions of Iran was described as Calomyscus behzadi sp. nov. The new species constituted a monophyletic clade in phylogenetic tree which its relationships are unresolved. A new karyotype was reported for the new species as 2N=44 and FNa=48. The results of multivariate statistical analyses also separated the new species from C. bailwardi and other recognized species of the genus Calomyscus. Based on the size + shape data, C. behzadi sp. nov. has shorter nasal than C. bailwardi, group D and C. grandis and narrower than C. baluchi but wider than C. hotsoni and C. elburzensis. Moreover, ccording to the shape data, the new species has shorter m2 than C. elburzensis, C. bailwardi, C. hotsoni, C. grandis and group D and narrower than C. bailwardi, C. grandis and C. baluchi. The new species was described from regions which had been known already as distribution area of C. bailwardi.

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