O’NEILL, M. W. *; GIBB, A. C.; Northern Arizona University; Northern Arizona University: Unexpected feeding asymmetries in the hogchoker, Trinectes maculatus

We investigate the purpose and function of extreme morphological asymmetry of the jaw apparatus in flatfishes. Previous research demonstrated that species with greater morphological asymmetry of the jaws display greater behavioral asymmetry during feeding. In general, behavioral asymmetry appears to focus prey capture through the blind side of the mouth and decrease the use of the eyed side of the mouth. In addition, flatfishes with greater jaw asymmetry produce greater jaw flexion toward the substrate. These behaviors may be a result of morphological adaptations for feeding on benthic organisms and appear to �aim� prey capture towards the substrate. We used the hogchoker, the most asymmetrical flatfish studied to date, to test the hypothesis that increasing jaw asymmetry generates increased jaw flexion and gape asymmetry. Hogchokers do have extreme gape asymmetry, with the blind side used exclusively for prey capture. However, the mechanism that produces the asymmetry is markedly different from that described for other flatfishes. The symphysis of the lower jaw displays no flexion and remains parallel to the sagittal plane during feeding. In previously studied fishes, the vomer, a �launching pad� of the upper jaw, inclines out of the sagittal plane and directs the upper jaw towards the substrate. In hogchokers, the vomer is oriented along the sagittal plane and does not aim the upper jaw towards the substrate. Upper jaw protrusion is minimal on the eyed side, and the blind side upper jaw elements swing towards the substrate. This specializes hogchokers for benthic feeding by directing suction towards the substrate and minimizing eyed side mouth opening. These differences in feeding mechanism asymmetries may imply a more distant phylogenetic relationship between more asymmetrical species and less asymmetrical species than previously thought.