Meeting Abstract
The cylindrical jawless feeding apparatuses (JFA) of hagfish and post-metamorphic lamprey, which include toothplates, associated muscles and cartilages, are traditionally referred to as “rasping tongues” due to the complex arrangements of muscle fibers that power the cyclic protraction-retraction motions of the toothplates. These toothplates are highly effective at grasping and piercing tissues, thus their motions might be more appropriately referred to as biting. Most biting systems include a pair of occluding tooth-bearing beams (e.g. jaw bones) connected by sturdy, compression-resistant joints. When employed, the biting system forms a closed kinematic loop, in which the reaction forces of those applied between the teeth are transmitted through the jaw joint. “Biting” can be a problematic term for jawless feeding systems because the retracting toothplates lack an obvious opposing element resembling an upper jaw; Toothplates applied to a surface without such opposing resistance, should simply push the animal away from the surface. This study 1) demonstrates how hagfish and lamprey supply their JFAs with a closed kinematic loop and thus implement true biting, and 2) compares structural and functional traits of the JFA in both taxa. Our survey of the literature and our own gross and histological anatomical descriptions indicate that hagfish and lamprey furnish an opposing element and close the kinematic loop in radically different ways: Lampreys use the adhering suction of their oral discs to counter the force of their rasping tongue whereas hagfish employ whole body knots to generate the required leverage.
