Hagfish slime expands ten thousandfold in under a second
Jawless Myxini keep a skull yet almost no backbone—the only living animals built that way—and fight with mucus. Released in seawater, their fibrous slime swells about ten thousand times in 0.4 seconds, clogging predator gills until the hagfish knots itself free from head to tail.
Genetics places them with lampreys in Cyclostomi, closer to each other than to jawed vertebrates. Stem hagfish appear by the Late Carboniferous around 310 million years ago; modern forms show up mid-Cretaceous near 100 million years ago. Typical length is about 50 centimetres; Eptatretus goliath has reached 127 centimetres, while some Myxine stay under 18. Loose sock-like skin, keratin tooth plates on a protracting cartilage, six or eight barbels, and eyespots without lenses define the look. Nearly a third of blood volume can sit in the skin sack.
Thread keratins stretch from alpha helices toward stiffer beta sheets; recombinant fibres have hit elastic moduli near 20 GPa, tempting body-armour researchers as a spider-silk alternative. Viscosity rises in elongational flow—bad for suction-feeding gills—and falls in shear, helping the travelling knot scrape mucus away. A 2017 Highway 101 spill of 7,500 pounds of hagfish coated road and car alike. They endure 36 hours in oxygen-free water, breathe through five to sixteen gill-pouch pairs, and may respire through skin while buried in anoxic mud.
Blood pressure ranks among the lowest in vertebrates, yet blood volume is about 17 millilitres per 100 grams of mass—the highest among chordates. Fluid balance is crude: rising extracellular volume raises pressure, and kidneys dump excess. They are the only known vertebrates isosmotic with seawater, plasma more like marine invertebrates. Accessory auxiliary hearts assist circulation; true cardiac innervation was confirmed after early doubts. Horizontal and vertical muscle septa are absent, so bite force and gape can exceed similar jawed fish even while jaws still snap faster.
Source: Hagfish
