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Functional Morphology of Pufferfish Inflation: Mechanism of the Buccal Pump
Peter C. Wainwright, Ralph G. Turingan and Elizabeth L. Brainerd
Vol. 1995, No. 3 (Aug. 18, 1995), pp. 614-625
Stable URL: http://www.jstor.org/stable/1446758
Page Count: 12
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The mechanism of the buccal pump used to fill the stomach with water during inflation behavior was studied in the striped burrfish, Chilomycterus schoepfi. The movement patterns of the pectoral girdle and the anterior region of the hyoid apparatus were inferred from simultaneous impedance and buccal pressure recordings. Impedance was measured between two electrodes; a stationary electrode implanted in the roof of the mouth and a second electrode implanted either in the anterior tip of the cleithrum or the musculature surrounding the anterior end of the hyoid apparatus. In addition, simultaneous buccal pressure and electromyographic (EMG) recordings were made during inflation sequences to determine the activity patterns of eight cranial muscles. Impedance recordings indicate that buccal expansion is caused by synchronous posteroventral rotation of the hyoid apparatus and the pectoral girdle, whereas buccal compression is accomplished by hyoid and pectoral girdle anterodorsal rotation. EMG data revealed that periods of reduced buccal pressure occurring at the onset of each inflation cycle were associated with activity of several muscles that open the mouth (levator operculi, dilatator operculi), depress the hyoid apparatus (hyohyoideus abductor, sternohyoideus), and retract the pectoral girdle (levator pectoralis). Periods of positive buccal pressure, during which water was forced into the stomach, were associated with muscular activity indicating mandibular adduction (adductor mandibulae), hyoid protraction (protractor hyoideus), and pectoral girdle protraction (protractor pectoralis). The key components of the buccal pump that, among tetraodontiform fishes, are derived for the Diodontidae plus the Tetraodontidae are the highly kinetic joint between the cleithrum and supracleithrum which permits extensive pectoral girdle protraction and retraction and the massively developed hyohyoideus abductor muscle that flexes a joint between the ceratohyal and the first branchiostegal ray, providing a novel mechanism of buccal floor depression.