Fig. 1. The sound-producing morphology of the California spiny lobster (Panulirus interruptus). A pair of plectrums (pink), an extension off each antenna, rub posteriorly over the files (dark red) to produce sound. The green arrow indicates the direction of the plectrum's movement when producing sound. Inset: a mass-and-spring representation of the acoustic stick–slip mechanism found in spiny lobsters (Patek, 2002; Patek, 2001). The plectrum (pink) is modeled as a moveable component with a mass sandwiched between two springs. The plectrum moves across the file (dark red), which is fixed in place. Each time the plectrum slips, a pulse of sound is produced. Movie 1 and Movie 2 in supplementary material show sound production and associated morphology, respectively.