Muscle Activity Patterns and Feeding Kinematics in Atlantic Hagfish (Myxine glutinosa)
Erick J. Maravilla
Adam P. Summers
We investigated motor patterns of the three largest muscles in the hagfish feeding apparatus: the deep protractor muscle (DPM), clavatus muscle (CM), and tubulatus muscle (TM). The anatomy of the DPM and CM suggests they respectively protract and retract the dental plate. Bipolar electrodes were implanted in anesthetized Myxine glutinosa. After recovery, we simultaneously videotaped behaviors and muscle activity patterns from the feeding specimen. Ingestion required three gape cycles (dental plate protraction-retraction events), and intraoral transport required four gape cycles. Percutaneous implantation of electrodes did not inhibit normal feeding behaviors. Time to maximum gape was significantly longer during transport events than capture events. Gape cycle and dental plate retraction times were similar in both capture and transport. The DPM was active during protraction, while the CM and TM were active during retraction. In both capture and transport phases, the DPM had longer bursts (414 ms) than the CM (308 ms) and TM (255 ms). For each muscle, burst duration was similar in both capture and transport phases. All muscles were active during every gape cycle in the capture phase. In the transport phase, the DPM was active in all gape cycles, while the CM and TM were active during the first two gape cycles. We propose TM activity during retraction provides a fixed point for the CM to retract the dental plate. Decreased TM and CM burst frequencies during transport phases raise the possibility that elastic recoil of the CM tendon is sufficient to passively retract maximally protracted dental plates.