Hypancistrus can be distinguished externally from most other hypostomines by having larger and fewer teeth on the dentary relative to the teeth on the premaxilla. Different numbers of teeth on the dentary and premaxilla are found in many loricariids, so this character is not always diagnostic (Armbruster 2002). The genus is diagnosed by the unique presence of a wide anterior separation between the metapterygoid and the lateral ethmoid, and a sharply angled adductor palatini crest. It also lacks the lateral wall of the metapterygoid channel (Armbruster 2002).