Fig. 1. The sound-producing mechanism found in the Caribbean spiny lobster Panulirus argus. The plectrum is a medial extension of the base of each antenna that rubs over a file, located on each side of the antennular plate. The flap extends posteriorly from the edge of the plectrum and is not necessary for sound production (see Discussion). The plectrum ridges, part of the stridulatory membrane, are confined to the ventral surface of the plectrum. Image © Sally J. Bensusen/courtesy Natural History Magazine.