Posterior to the mouthparts, the dominant ventral feature of the larval head is a plate, which is usually toothed. The terminology for this plate depends upon hypoteses concerning its origin, with earlier disparate views giving rise to the older terms labium or hypostomium (hypostoma). However, Saether argued convincingly for the use of Craig's term mentum, and he established that the plate is double-walled and of dual origin.