Meeting Abstract
The slack skin of hagfishes may enhance maneuverability (e.g. body knotting or squeezing through tight spaces) and resist puncture. Hagfish skin facilitates forming and manipulating body knots because its baggy fit decouples the otherwise restrictive skin from the muscles and viscera of the body core. Previously, the skin of the Pacific hagfish (Eptatretus stoutii) has been shown to be as strong and stiff as the taut skins of other fishes, but with one difference: hagfish skin is significantly more compliant in the circumferential axis. This anisotropy may facilitate extreme body torsions needed to produce a knot. It is unclear if the morphology and material properties are conserved across the skins of other hagfishes. Here, we use quasi-static uniaxial tensile tests and histology to investigate the material properties and morphology of the skins from four hagfish species, two Eptatretines (E. stoutii, E. springeri) and two Myxinines (Myxine glutinosa, and M. hubbsi). Across all hagfish species, the skins are comparable in thickness, stiffness, strength, extensibility, and toughness. However, in contrast to E. stoutii skins, the skins of all other hagfish species tested are isotropic, being equally resistant to strains applied along longitudinal and circumferential body axes. Histological data show an abundance of contractile fibers in the dermis of the Eptatretines but a conspicuous absence in the dermis of the Myxinines. These hagfish species exhibit notably different knotting and resting behaviors, with E. stoutii coiling their bodies at rest and forming the tightest body bends during knotting. We propose that these behavioral differences across species may be associated with variation in the form and function of the skin and notochord.
