Gnathosomal interlocking apparatus and remarks on functional morphology of frontal lobes of eriophyoid mites (Acariformes, Eriophyoidea).

Comparative study of eriophyoid mite gnathosomata using different microscopic techniques shows presence of new dorsoproximal structures (here described as "interlocking apparatus"), which could consolidate mouthparts in rest (non-feeding) position and during feeding actions. Four types of the interlocking apparatus are described. Differences in the interlocking mechanisms coincide with the results of recent molecular phylogenetic studies of Eriophyoidea and provide additional support for the major clades revealed in those studies. Comparative analysis on the morphology of the frontal lobe of the prodorsal shield shows that mechanical protection of the motivator surrounding area and interlocking apparatus are possibly the primary function of the frontal lobe. Unusual shapes of the frontal lobe in selected eriophyoids (elongated, broadened, notched lobes) might result from additional functions that the frontal lobe can perform, e.g. providing additional guide for palps and stylets, or hermeticity of the space between dorsoproximal palpcoxae during feeding.