Fig. 3. Models of the antennal joints found in sound-producing and non-sound-producing spiny lobsters. (A) In non-sound-producing palinurids, the joint between the antenna and cephalothorax is limited to one degree of freedom (left, adapted from Wainwright et al., 1976) and has an axis of rotation aligned between the two joint articulations (right). (B) In sound-producing palinurids, the same joint has multiple degrees of freedom (left), which is permitted by the loss of the medial joint articulation. With only one joint articulation, the medial process of the antenna (the plectrum) can generate translational motion over the file.

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