Fig. 9. A comparison of plectrum and file morphology in Panulirus argus and Palinurus elephas. (A) Palinurus elephas (carapace length 145 mm); a dorsal view of the surface the lobster's right file (18 mm long); anterior is towards the bottom of the page, lateral is to the left of the page. Covering the file are microscopic shingles with anteriorly projecting edges (inset). Scale bar, 25 µm. On the lateral side of the file is a long groove. (B) Palinurus elephas; the ventral surface of the lobster's right plectrum (6 mm wide); lateral is to the right of the page. The plectrum consists of a hemisphere of soft tissue ridges, the stridulatory membrane, and the flap extends from the posterior edge of the stridulatory membrane. These ridges rub against the file; the long axis of the ridges is parallel to the long axis of the file and thus parallel to their motion over the file. A knob, adjacent to these ridges, fits into the groove on the file. The plectrum rubs posteriorly over the shingle edges (towards the top of the page). The scanning electron micrograph (inset) shows the posterior limit of the plectrum ridges on the stridulatory membrane. Scale bar, 50 µm. (C) The same view as in A for the file (14 mm long) and shingles of Panulirus argus (85 mm carapace length). Scale bar, 25 µm. (D) The same view as in B for the plectrum (4 mm wide) and plectrum ridges of Panulirus argus. Scale bar, 50 µm.

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