Two new fossils belonging to the extinct arachnid order Trigonotarbida are described from uppermost Carboniferous (Gzhelian, Upper Pennsylvanian) strata of the Villablino and El Bierzo basins (Castilla y León; NW Spain). These discoveries represent the second and third Spanish records of this arachnid order and are among the oldest arachnid records known from the Iberian Peninsula. They also represent the first evidence of arachnids from the Villablino and El Bierzo basins. One fossil consists of an almost complete individual including the prosoma, opisthosoma, legs and pedipalps but its preservation in ventral view makes unequivocal identification difficult. Comparison with other material favours its assignment to Aphantomartus sp. (Aphantomartidae). The second specimen consists of a prosoma and opisthosoma preserved in dorsal view and is assigned to Aphantomartus areolatus. These two arachnids were preserved alongside several plant remains referable to ferns (Polymorphopteris polymorpha, Polymorphopteris integra, Nemejcopteris feminaeformis and Oligocarpia leptophylla), seed-ferns (Neuropteris ovata) and lycophytes (Cyperites bicarinatus). The abundance and diversity of co-occurring plant remains are consistent with the other known Spanish Aphantomartus record, which is also preserved in association with several plant fossils. Based on the new occurrences, we infer that Aphantomartus favoured humid, broad-leafed, evergreen forest habitats that provided a diverse array of food and shelter.