Meeting Abstract

P2.74  Jan. 5  Morphology and kinematics of the hagfish feeding apparatus CLARK, A/J*; SUMMERS, A/P; Univ. of California, Irvine; Univ. of California, Irvine aclark@uci.edu

We examined the morphology and kinematics of the feeding apparatus of two hagfish species, Eptatretus stoutii and Myxine glutinosa. During feeding, a pair of cartilaginous dental plates exit and enter the oral cavity by two protractor muscles and three retractor muscles, respectively. The basal plate, which is ventrally situated in the anterior tenth of the body, supports these feeding structures. Both species are morphologically distinguishable in total dental cusp number (40 in E. stoutii and 34 in M. glutinosa) and gill pouches (12 in E. stoutii and 6 in M. glutinosa). Morphometrics data were collected from 8 E. stoutii and 8 M. glutinosa. Despite differences in total dental cusp number, the dental plates are similar in length (9.4mm in E. stoutii and 8.5mm in M. glutinosa) and width (12.5mm in E. stoutii and 11.9mm in M. glutinosa). Mean basal plate lengths were 12.6% of total length in E. stoutii and 10.7% in M. glutinosa. Feeding kinematics data from 4 E. stoutii and 5 M. glutinosa were compared with similar kinematics variables from earlier investigations on gnathostome feeding. We propose a pulley model for dental plate protraction and retraction, which does not differ between species. There were no significant differences in bite cycle time (995ms), maximum gape time (332ms), and maximum protraction angle (175 degrees) between the two species. Dental plate mechanics are unaffected by the different branchial morphologies in E. stoutii and M. glutinosa. We propose that functional constraints of jawless feeding are longer bite cycle times and maximum gape times that would preclude feeding on elusive prey. Conversely, the hagfish feeding apparatus permits dental plate protraction angles to exceed gnathostome gape angles, suggesting the limited gape angle in gnathostomes is a functional tradeoff for having jaws.