[1] A fossil assigned to this genus was found at Montceau-les-Mines, France, in ironstone concretion deposits of Late Carboniferous (Stephanian) age, about 305–299 million years old.

Montceau fossils are generally preserved in such a way that fine details can be observed and three-dimensional analysis is possible.

The chelicerae are shaped like a clasp-knife, i.e. with the fang at the end folding back into the part to which it is attached.

The species name honours Martin David Brasier for his contributions to the study of ancient life.

[1] Based on its overall morphology, Idmonarachne was considered to belong to the Serikodiastida, a clade of tetrapulmonate arachnids capable of making and using silk, although the presence of silk-producing spigots was not demonstrated.