Meeting Abstract
Hagfish use a poorly understood feeding apparatus mechanism to protrude and retract a dental plate for rasping chunks of tissue from prey for ingestion. Retraction is achieved by activating a complex soft tissue mechanism found in the posterior half of the feeding apparatus. In this study, we describe the anatomy of this muscular hydrostat by examining the muscle and connective tissue fiber organizations in the feeding apparatuses of nine Pacific (Eptatretus stoutii) and six Atlantic (Myxine glutinosa) hagfishes. Paraffin histological techniques were used to prepare serial sections. Structural components were manually segmented from these digitized sections and fitted to high-resolution 3D scans (Arctec Space Spider) of the whole feeding apparatus. Our analysis of the soft tissue fiber orientations allowed us to develop a number of functional hypotheses: (i) The tubulatus muscle is not a simple sheath formed of circumferential muscle fibers as previously reported. It is a unique tubular muscle with bi-pinnate muscle fiber orientations that originate from a longitudinal dorsal tendon and insert on a ventral one. Activation may cause the muscle to become longer and skinnier and also cause the dorsal and ventral surfaces to shear relative to each other. (ii) The clavatus muscle includes longitudinal muscle fibers that may generate direct force used in dental plate retraction. (iii) Activation of the complex fiber organization of the perpendicularis muscle likely causes the posterior end of the clavatus to deform laterally and function as a stopper knot to prevent the clavatus from sliding through the tubulatus. While electromyographic recordings of active muscles have been unsuccessful, video recordings of preliminary electrostimulation experiments confirm these functions.
