The described male and female have an abdomen mottled brown and beige.
In the described male and female, the carapace, long jaws and legs are reddish brown. Some leg joints are yellowish white.
Eriauchenus harveyi has a long spine near the base of each elongated jaw, projecting approximately perpendicular to its surface. Two short spines on the crown of the head contrast with these longer jaw spines.
The described male measured about two millimetres in body length and 1.30 millimetres in jaw length. The spine arose 0.15 millimetres from the jaw base. In the female, a similarly projecting spine arose 0.17 millimetres from the base.
The anterior median eyes lie virtually flush with the surrounding surface. Microscopic description documents the placement of eyes and spines within this small spider’s unusual head and jaws.
An extinction-risk assessment has not been added yet.
For the Andringitra region, the park authority identifies clearing, slash-and-burn agriculture and vegetation fires among environmental pressures. It reports expanded patrols and fire-area mapping in 2024. Repeated surveys of rainforest litter at historical collecting localities could help document this spider’s occurrence.