Meeting Abstract
The spectacular knot tying behaviors of hagfishes are a product of their complex axial muscles, loose-fitting skin, and flexible bodies devoid of vertebrae. Slack skins are peculiar body coverings in fishes and other aquatic animals that possess taut skins that are mechanically important in retaining body shape while being flexible enough to permit the body deformations necessary for movement. Like other fish skins, hagfish skins are multilayered biological composites. However, the skins of Pacific hagfish Eptatretus stoutii are more compliant circumferentially, while other fish skins are more compliant longitudinally. Body knotting and loose-fitting skins are featured across many species of hagfish, including the well-studied Atlantic and Pacific hagfish, each representative of the two major subfamilies of the Myxinidae: the Myxininae and Eptatretinae. The resting positions, or “postures,” of these demersal fishes can be coiled (e.g. Pacific hagfish) or stretched (e.g. Atlantic hagfish). This difference in posture could pertain to differences in the material properties of key anatomical structures like the notochord and the skin. We present the morphology and material properties of the skins from two Myxinines: the Atlantic hagfish Myxine glutinosa and Myxine hubbsi and compared them with data gathered from E. stoutii. Skin samples oriented in longitudinal and circumferential body axes, were subjected to quasi-static uniaxial tensile tests to failure. Skins from both Myxinines are isotropic but comparable in thickness, stiffness, strength, extensibility, and toughness to anisotropic E. stoutii skins. The biomechanical variation in these skins appears to be related to the variation in resting postures and knotting kinematics across species.
