A. piatnitzkyi is reported from three specimens, giving a body length between 16–18 mm (0.63–0.71 in).
The holotype, recovered from the Ventana Formation of the Neuquén Basin in Argentina is currently preserved at the Bernardino Rivadavia Natural Sciences Museum palaeoentomological collection.
The head capsule is slightly ovoid, being a little longer than it is wide and having elongated mandibles that are notably shorter than the head.
As with A. smekali, the mesosoma is massive, being between 1.7-1.8 times as long as it is tall.
 The legs are like those of the other species, being long and thin.
Unlike the other species, the petiole of A. piatnitzkyi does not have a constricted post-petiole.
A. piatnitzkyi is reported from three specimens, giving a body length between 16–18 mm (0.63–0.71 in). The holotype, recovered from the Ventana Formation of the Neuquén Basin in Argentina is currently preserved at the Bernardino Rivadavia Natural Sciences Museum palaeoentomological collection. The head capsule is slightly ovoid, being a little longer than it is wide and having elongated mandibles that are notably shorter than the head. As with A. smekali, the mesosoma is massive, being between 1.7-1.8 times as long as it is tall.  The legs are like those of the other species, being long and thin. Unlike the other species, the petiole of A. piatnitzkyi does not have a constricted post-petiole.
Archimyrmex