Meeting Abstract
Hagfish are jawless, invertebrate chordates that may compensate for a lack of opposable jaws by employing leverage created by forming and manipulating body knots during feeding. Hagfish can also use knots to clean off mucous and to escape confined spaces. The mechanical characterization of knotting has not been well described because it is difficult to consistently control and stimulate this behavior experimentally. Here we study the knots formed by Eptatretus stoutii (Lockington, 1878) through the use of a custom jig that holds a sedated hagfish securely using an elastic membrane. Once the hagfish awakens it attempts to escape by rolling and swimming backwards. To escape however, the animal consistently forms a figure 8 knot and works it anteriorly to leverage its head out. We use this setup to a) identify common steps in knotting, b) describe knotting physical characteristics, including handedness and radii of loops, c) record three-dimensional kinematic parameters, and d) estimate head retraction forces. This behavior was recorded using two high-speed cameras (Phantom Miro320; Wayne, NJ; 350Hz) that were set at 90° from each other. After the kinematic analysis of video frames from 22 knotting events performed by 11 animals (using Tracker V. 4.90), we found that E. stoutii preferentially form right-hand knots (77%) and that the knotting process could be decomposed into 13 characteristic steps. We were able to record some preliminary measurements of head retraction force; it is highly variable (0.8-9 N, 17-41 N/kg body weight), and, interestingly, much lower than what is required to pull a semisolid plug of similar diameter from the membrane (28N). Further investigations are required to assess whether these knotting characteristics are species specific or represent generalized hagfish behavior.
