The mandible (from Latin: mandibula or mandĭbŭ-lum, a jaw)  of an arthropod is a pair of mouthparts used for either for biting, cutting and holding food. The last three cephalic segments, together with the three most anterior thoracic segments (all of the cephalothorax), house the external mouthparts. From anterior to posterior these are the mandibles, maxillules, maxillae and then the three pairs of thoracic maxillipeds. These are all biramous except for the mandibles and maxillules.  Mandibles are often simply referred to as jaws. Maxillipeds are appendages modified to function as mouthparts. Hermit crabs are often seen grooming their eyes with their maxillipeds much like a cat uses it’s paw to clean its face.
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1 Latin Dictionary Founded on Andrews’ edition of Freund’s Latin dictionary revised by Charlton T. Lewis, Ph.D. and. Charles Short, LL.D. Oxford. Clarendon Press. 1879.
2. Dardanus megistos by Storm Martin 2012