Meeting Abstract
18.1 Jan. 5 Hyoid mechanics and muscle function during feeding in white-spotted bamboo sharks, Chiloscyllium plagiosum. RAMSAY, J.B.*; WILGA, C.D.; Univ. of Rhode Island; Univ. of Rhode Island jasonramsay@mail.uri.edu
The feeding apparatus in white-spotted bamboo sharks, Chiloscyllium plagiosum exhibits many characters associated with suction feeding such as labial cartilages to occlude the lateral portions of the gape and hypertrophied hypobranchial musculature to power hyoid depression against high negative pressures generated in the buccal cavity. The medial hyoidiomandibular ligament may assist in lower jaw depression by harnessing and amplifying force generated by the coracohyoideus (CH) and coracoarcualis (CA) and transferring it to the lower jaw to assist the coracomandibularis (CM) in generating posteroventral rotation of the mandible. Hyoid, upper and lower jaw kinematics and fascicle shortening in the CM and CH were quantified using high-speed video and sonomicrometry, while muscle activity and buccal pressure were recorded simultaneously. Peak active shortening of the CM occurs at ~50% of fast jaw opening, just after the onset of buccal pressure decrease, while peak gape occurs just prior to passive CM lengthening. The CH lengthens prior to shortening and hyoid depression. CH lengthening peaks midway through slow hyoid depression, while fast CH shortening peaks simultaneously with peak hyoid depression and jaw closure. Initial lengthening of the CH may be due to shortening of the more caudal in-series CA, thereby preloading the CH. Peak CM shortening, onset of CH shortening and depression of the hyoid occur simultaneously. Consequently, the CM initiates lower jaw depression while the CH and CA drive the jaw and hyoid to peak depression. The hyoidiomandibular ligament in C. plagiosum, also present in most orectolobiform species, appears to be a biomechanical link coupling lower jaw and hyoid depression that is convergent with the mandibulohyoid ligament in teleosts, the most derived bony fishes.
