Meeting Abstract
Hagfishes are jawless fishes that grasp and swallow food items with protractible dental plates. A dental plate (DP) is composed of keratinous teeth mounted on a thin wing-like cartilaginous plate housed within the anterior half of the hagfish feeding apparatus (HFA). Cyclic protraction-retraction of the DP is supported ventrally by relatively thick cartilaginous basal plates (BP). As the DP protracts from the mouth, it unfolds like an opening book revealing the teeth, then during retraction, the DP folds medially like a closing book as it pulls food into the mouth. Protraction is mostly powered by a quartet of strap-shaped muscle rami that originate from the ventral surface of the BP and insert onto the anterior margin of the DP. Retraction is powered by a muscular hydrostat in the posterior half of the HFA. The cylindrical hydrostat contains a three-dimensionally complex arrangement of longitudinal, semicircular, and transverse muscle fibers. Visualizing and reconstructing this morphology is challenging because the HFA is almost entirely composed of soft tissues. We used diffusible iodine-based contrast-enhanced micro-CT scans to successfully visualize and reconstruct the 3D morphology of the HFA from a Pacific hagfish. In Avizo, we segmented the dentition and cartilages and inspected the 3D arrangement of muscle fascicles and connective tissues in the HFA. Dice-CT scans clearly illustrate the 3D complexity of the muscular hydrostat and corroborate recently published histologically based anatomical reconstructions. These data also show that the cartilages and teeth are either poorly interconnected or completely decoupled, suggesting that the anterior HFA can be readily deformed to accommodate various food items.
