Mandibles linear and elongate, their bases extremely closely approximated and with kinetic mode of action, each with an apical fork of 3 spiniform teeth that interlock at full closure. Preapical dentition sometimes present but often absent. Mandibles at full gape open to 170 degrees or more. Basal process of mandible a long curved spur that is minutely bifurcated apically; when mandibles fully closed the basal processess cross over and are ventral to the labrum and at the apex of the labio-maxillary complex; when fully open the mandibles are braced in that position by opposition of the basal processes alone. Trigger hairs arise from the mandibles (one from each); trigger hairs lie flat against margin when mandible closed, becoming erect as mandibles open. Palp formula 0,1. Labrum extremely reduced to vestigal, represented by a narrow Y-shaped sclerite; labrum not taking part in mandibular locking mechanism. Buccal cavity narrow, parallel-sided anteriorly; labio-maxillary complex narrow.
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