Abstract The baggy skins of hagfishes confer whole-body flexibility that enables these animals to tie themselves into knots without injury. The skin’s looseness is produced by a subcutaneous blood sinus that decouples the skin and body core and permits the core to contort dramatically without loading the skin in tension or shear. Hagfish skin represents a biological composite material comparable in strength and stiffness to the conventionally taut skins of other fishes. However, our understanding of hagfish skin is restricted to only one of 78 species: The Pacific hagfish Eptatretus stoutii. To determine if other hagfish share similar characteristics with E. stoutii, we measured material properties and compared histological data sets from the skins of four hagfish species: E. springeri, E. stoutii, Myxine glutinosa, and M. hubbsi. We also compared these material properties data with skins from the American eel, Anguilla rostrata. We subjected skin samples from all species to uniaxial tensile tests in order to measure strength, stiffness, extensibility, and toughness of skins stretched along longitudinal and circumferential axes. We also used a series of equibiaxial tensile tests on skin samples from E. stoutii, M. glutinosa, and A. rostrata to measure stiffness of skins simultaneously strained along both axes. Significant results of uniaxial and biaxial tests show that the skins from Eptatretus are anisotropic, being stiffer in the longitudinal axis, and more extensible than the isotropic skins of Myxine. Skins of A. rostrata were stiffer in the circumferential axis and they were stronger, tougher, and stiffer than all hagfish skins examined. The skins of Eptatretus are histologically distinct from Myxine skins and possess arrays of fibers that stain like muscle. These interspecific differences across hagfish skins show a phylogenetic pattern with knotting kinematics and flexibility; both genera belong to distinct but major subfamilies within the Myxinidae, and Eptatretus is known for creating and manipulating a greater diversity of knotting styles than Myxine.

中文翻译：

---

盲鳗皮肤的比较生物力学：材料、形态和运动的多样性

摘要 盲鳗的宽松皮肤赋予全身柔韧性，使这些动物能够将自己打结而不会受伤。皮肤松弛是由皮下血窦产生的，它使皮肤和身体核心分离，并允许核心剧烈扭曲，而不会使皮肤承受张力或剪切力。盲鳗鱼皮代表了一种生物复合材料，其强度和刚度可与其他鱼类的传统绷紧皮肤相媲美。然而，我们对盲鳗皮肤的了解仅限于 78 种物种中的一种：太平洋盲鳗 Eptaretus stoutii。为了确定其他盲鳗是否与 E. stoutii 具有相似的特征，我们测量了材料特性并比较了四种盲鳗鱼皮的组织学数据集：E. springeri、E. stoutii、Myxine glutinosa 和 M. hubbsi。我们还将这些材料特性数据与美洲鳗鱼 Anguilla rostrata 的皮进行了比较。我们对所有物种的皮肤样品进行了单轴拉伸试验，以测量沿纵向和圆周轴拉伸的皮肤的强度、刚度、延展性和韧性。我们还对来自 E. stoutii、M. glutinosa 和 A. rostrata 的皮肤样本进行了一系列等双轴拉伸试验，以测量沿两个轴同时拉伸的皮肤的刚度。单轴和双轴试验的显着结果表明，Eptaretus 的蒙皮是各向异性的，在纵轴上更硬，比 Myxine 的各向同性蒙皮更具延展性。A. rostrata 的皮肤在圆周轴上更硬，它们比所有检查的盲鳗皮肤更结实、更坚韧和更硬。Eptaretus 的皮肤在组织学上与 Myxine 皮肤不同，并且拥有像肌肉一样染色的纤维阵列。盲鳗皮肤的这些种间差异显示出具有打结运动学和灵活性的系统发育模式；这两个属都属于粘菌科内不同但主要的亚科，而 Eptaretus 以创造和操纵比粘菌属更多样化的打结方式而闻名。