[5] He based the original description of this species on specimens of both sexes, collected from Lyons-la-Forêt and from the summit of Puy-de-Dôme, both locations in France.

[5] In 1914, the Austrian myriapodologist Carl Attems deemed Gnathomerium to be a junior synonym of Arctogeophilus,[6] a taxon originally proposed by Attems in 1909 as a subgenus of the genus Geophilus but elevated to the status of genus in 1910 by Ribaut.

Furthermore, as in other species in this genus, the side pieces of the labrum meet in front of the middle part.

[5][12][13] The only other Arctogeophilus species found in western Europe, the German species A. wolfi, closely resembles A. inopinatus, with a similar shape for the head and the body, a similar distribution of pores on the ultimate legs, ultimate legs that are much longer than the preceding legs, and anal pores on the telson.

[5][10] The species A. inopinatus has been observed in several regions of mainland France, including Brittany, Haute-Normandie, Auvergne,[14] and the Morvan.

[16] Authorities have expressed some doubt regarding the reported presence of this species in Luxembourg.