Acanthogonatus mulchen is a mygalomorph spider of Chile, named after its type locality: Alto Caledonia, east of Mulchén, Region VIII (Bío Bío Region).

It differs from A. tolhuaca in the spermathecae having a less pronounced notch and the glandular areas on each side joining in the middle.

It is larger (A. mulchen has a cephalothorax length of up to 13.2 millimetres (0.52 in), and a total length of 35.05 millimetres (1.380 in)) and differs from A. brunneus by its uniformly colored abdomen.

It is found in densely silk-lined burrows, between 15 and 20 millimetres (0.59 and 0.79 in) wide, which originate from under stones or at the base of trees.

The burrow's mouth is funnel-like, with white silk extending so as to form a sort of collar.