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A new species of the hagfish genus Eptatretus (Myxinidae) is described based on a single female specimen, 296 mm total length, collected from the Bahamas, off southern Grand Bahama Island, Northwest Providence Channel, between depths of 560 and 591 m. The new species is distinguished from its congeners by having five pairs of well-spaced gill apertures arranged in a nearly straight line, a 3/2 multicusp pattern of teeth, 54 total tooth cusps, 18 prebranchial slime pores, 4–5 branchial pores, 47–49 trunk pores, 82–85 total pores, and two bilaterally symmetrical nasal-sinus papillae. We also discuss the taxonomy of a specimen from Suriname provisionally named as Eptatretus sp. by Shimizu. A distribution map and an updated identification key for all species of Eptatretus and Rubicundus from the western Atlantic are provided. [ABSTRACT FROM AUTHOR]

Synopsis Intermediate filaments are filaments 10nm in diameter that make up an important component of the cytoskeleton in most metazoan taxa. They are most familiar for their role as the fibrous component of [alpha]-keratins such as skin, hair, nail, and horn but are also abundant within living cells. Although they are almost exclusively intracellular in their distribution, in the case of the defensive slime produced by hagfishes, they are secreted. This article surveys the impressive diversity of biomaterials that animals construct from intermediate filaments and will focus on the mechanisms by which the mechanical properties of these materials are achieved. Hagfish slime is a dilute network of hydrated mucus and compliant intermediate filament bundles with ultrasoft material properties. Within the cytoplasm of living cells, networks of intermediate filaments form soft gels whose elasticity arises via entropic mechanisms. Single intermediate filaments or bundles are also elastic, but substantially stiffer, exhibiting modulus values similar to that of rubber. Hard [alpha]-keratins like wool are stiffer still, an effect that is likely achieved via dehydration of the intermediate filaments in these epidermal appendages. The diverse mechanisms described here have been employed by animals to generate materials with stiffness values that span an impressive eleven orders of magnitude.

The activity of several enzymes in the visceral retia of Thunnus thynnus bluefin tuna was analyzed to characterize the patterns of enzyme compensation. Quantitative analysis of the enzymes involved in amino acid metabolism and anaerobic carbohydrate metabolism indicated the positive correlation between adaptation temperature and the enthalpy of activation. The positive thermal compensation that was exhibited by the enzymes was also achieved via differences in enzyme concentration along the visceral retia.

A test of biochemical symmorphosis in a heterothermic tissue: bluefin tuna white muscle. Am J Physiol Regulatory Integrative Comp Physiol 280: R108-R114, 2001.--To test predictions of biochemical symmorphosis, we measured the activity of seven consecutive glycolytic enzymes at three positions along the heterothermic white muscle of the bluefin tuna. Biochemical symmorphosis predicts that adjustments in sequential enzyme concentrations along a thermal gradient should occur as a function of the thermal sensitivity of the enzymes to ensure that no one enzyme in the pathway is in excess at any point along the gradient. We found no evidence for adjustments in enzyme quantity or quality along the thermal gradient, as well as no evidence for the prediction that the more temperature-sensitive enzymes would exhibit more dramatic compensation. Conservation of glycolytic flux in the cold exterior and warm interior muscle may be achieved by the near insensitivity of glyceraldehyde-3-phosphate dehydrogenase to temperature in this tissue. This may have the added benefit of moderating flux during seasonal or transient changes in the thermal gradient. According to the strictest application of biochemical symmorphosis, such a mechanism represents adequate, yet suboptimal design. temperature; Thunnus; enzyme; fish; glycolysis; lipid

Fibers are ubiquitous in biology, and include tensile materials produced by specialized glands (such as silks), extracellular fibrils that reinforce exoskeletons and connective tissues (such as chitin and collagen), as well as intracellular filaments that make up the metazoan cytoskeleton (such as F-actin, microtubules, and intermediate filaments). Hagfish gland thread cells are unique in that they produce a high aspect ratio fiber from cytoskeletal building blocks within the confines of their cytoplasm. These threads are elaborately coiled into structures that readily unravel when they are ejected into seawater from the slime glands. In this review we summarize what is currently known about the structure and function of gland thread cells and we speculate about the mechanism that these cells use to produce a mechanically robust fiber that is almost one hundred thousand times longer than it is wide. We propose that a key feature of this mechanism involves the unidirectional rotation of the cell's nucleus, which would serve to twist disorganized filaments into a coherent thread and impart a torsional stress on the thread that would both facilitate coiling and drive energetic unravelling in seawater. [ABSTRACT FROM AUTHOR]

We used confocal microscopy and immunohistochemistry to characterize the morphology of the subcutaneous neurons and the innervation of the slime glands and striated muscles in the hagfish Myxine glutinosa. A rich plexus of 5HT-, ChAT- and TH-positive neurons is described in the capsule of the slime glands. These neurons, like those of the subcutaneous plexus, receive pericellular terminations from the axons of central cells. Capsular neurons receive innervation from 5HT-positive and nNOS-positive nerve fibres. Other nerve endings belonging to two separate nerve populations are identified in the striated muscles. They contain TH and nNOS immunoreactivity. Due to the lack of any topographical labelling, the cell origin and the projections of the neurons into the cranial and spinal nerves are unknown. This study provides anatomical evidence of multiple (5HT and nNOS) peripheral innervation of the neurons. However, it does not provide information about the function of these neurons in the hagfish. We suggest that hagfish neurons have a phylogenetic relationship with the spinal group of the dorsal cells of lampreys and the supramedullary cells of teleosts. [ABSTRACT FROM AUTHOR]

Hagfishes defend themselves from fish predators via the rapid deployment of a fibrous slime that adheres to and clogs gills. The slime transforms from a thick glandular exudate to a fully hydrated product in a fraction of a second through a process that involves the swelling and rupture of numerous mucin vesicles. Here we demonstrate that the vesicle membrane plays an important role in regulating the swelling of mucin granules, and provide evidence that the membrane contains proteins that facilitate the movement of ions and water molecules. By exposing isolated mucin vesicles to varying combinations of inorganic ions, organic compounds and membrane channel inhibitors, we found that the majority of hagfish mucin vesicles require Ca2+ to rupture. We also show that Ca2+-dependent rupture can be pharmacologically inhibited, which suggests a role for Ca2+-activated membrane transporters. We demonstrate that the aquaporin inhibitor mercuric chloride reduces the rate of vesicle swelling by an order of magnitude, which suggests that aquaporins facilitate the influx of water during vesicle deployment. Molecular evidence of two aquaporin homologues expressed in the slime glands further supports this idea. We propose a model of hagfish slime mucin vesicle rupture that involves Ca2+-activated transporters and aquaporins, and suggest that the presence of these proteins is an adaptation for increasing the speed of vesicle rupture and, consequently, the speed of the sliming response of hagfishes. [ABSTRACT FROM AUTHOR]