Meeting Abstract
Pacific hagfish Epatatretus stoutii are jawless invertebrate fishes known for employing spectacular whole body knotting movements for feeding and escape. This extreme body deformation depends on the flexibility that may be made possible by a relatively loose skin. This slack skin morphology results from the absence of myoseptal tendons that provides the tautness in other fish skins. The skin’s looseness and slimy surface texture may also prevent the teeth of predators from directly applying force to the body core, thus making the hagfish skin a puncture resistant “soft armor” reminiscent of a matador’s red cape. Skin samples oriented in longitudinal and circumferential axes were analyzed from E. stoutii and Apodichthys flavidus using quasi-static uniaxial tensile tests to failure, with additional samples collected for histological reconstructions. Our results show that hagfish skin is a relatively thick, anisotropic, multilayered composite material comprising a superficial thin and slimy epidermis, a middle dermis layer densely packed with fibrous tissues, and a deep hypodermis layer comprised of adipose tissue, which collectively is stiffer when pulled in the longitudinal than circumferential directions. The skins of both species studied are comparable in strength and stiffness, but gunnel skins are twice as resistant to circumferential strains than longitudinal strains. While these results show gunnel skin having characteristics of pressurized cylinder walls, many taut fish skins do not function this way, though their skins show greater resistance to circumferential strains than longitudinal strain. The anisotropy we observe in E. stoutii skin might be characteristic of loose fitting integument.
