Meeting Abstract

68.3  Tuesday, Jan. 6  Biomechanics of feeding in a jawless fish CLARK, A/J*; MARAVILLA, E/J; SUMMERS, A/P; Univ. of California, Irvine aclark@uci.edu

Despite lacking jaws and substantial rigid support for feeding muscles, hagfishes can forcefully grasp and ingest chunks of flesh from their prey. It is surprising that the amount and arrangement of hard and soft tissue in the hagfish feeding apparatus (HFA) does not constrain the transmission of forces produced by the musculature. When feeding, bilaterally folding dental plates repeatedly protrude from the mouth. Dental plate movement occurs over a rigid basal plate in a manner resembling a pulley system. The retractor muscles, which exert the most direct force on the dental plates, originate in the posterior 50% of the HFA where rigid support is absent. Determining how large magnitudes of force can originate from soft origins is important for understanding how hagfish feed. We investigated motor patterns of the three largest muscles in the HFA: the deep protractor muscle (DPM), clavatus muscle (CM), and tubulatus muscle (TM). Individuals normally used four gape cycles to ingest food and four gape cycles to intraorally transport food. We measured burst duration from each muscle, TM and CM onsets relative to the DPM (reference muscle), and onsets of each muscle relative to kinematic events. The DPM fired during protraction, while the CM and TM fired during retraction. CM burst duration significantly decreased during transport. Relative to DPM onsets, TM onsets preceded CM onsets by approximately 40 ms in both capture and transport stages. Burst onsets of the retractor muscles occurred either before or after the onset of retraction during capture, but usually followed the onset of retraction during transport. Our study corroborates anatomical predictions about DPM and CM function and demonstrates that activating the circumferentially arranged TM fibers around the CM produces a stiff origin for the generation of retractile forces.