With characters like the presence of a hypocone (fourth cusp) on the upper third premolar, the presence of a connection between the protocone and metaconule cusps on the second upper molar in only a few specimens, this species is intermediate between the slightly older Galerix symeonidisi and the slightly younger Parasorex pristinus.

The specific name, kostakii, honors Constantin "Kostaki" Theocharopoulos, who studied the cricetid rodents found at Karydia.

[2] In Komotini, a slightly younger site (assigned to zone MN 5) near Karydia, a single first upper molar (M1) of an unidentified Galerix species similar to G. kostakii has been found.

However, it also retains primitive, Galerix-like features, including the condition of p4 and the presence of a protocone-metaconule connection in some specimens.

This lineage may have evolved these traits, which may be adaptations to a herbivorous diet, convergently with Schizogalerix, which appears earlier in the fossil record.