[Polychaeta] Ventral jaw plate (in the order Eunicida).

[Crustacea ] Third pair of appendages; first pair of mouthparts; having a feeding function, do usually not show sexual dimorphism.

[Ostracoda] mandible (Ostracoda)

[Amphipoda] (Abbr. MD) a pair of appendages attached laterally to the mouth. The mandibles have powerful muscles and often solid anterodistal processes called incisors which are often strongly serrate. Right next to the distal "teeth" may be an articulated serrate accessory plate, the lacinia mobilis, which may be present on only one of the mandibles. A molar, with or without a grinding surface, often occurs on the medio-ventral surface of the mandible, but it may be reduced or absent. Most amphipods have a 3-articulated palp attached to the dorsolateral surface of the mandible. In Hyperiidea this palp is often absent, or may be present in the male and absent (or, more rarely, reduced to 1 or 2 articles) in the female of the same species. mandible (Amphipoda)

Alternative form for mandible : [Crustacea] md (abbrev.).