Slime and fibers protect: hagfish
Glands of hagfish protect it from predators by secreting a complex material of fibers and rapid water-absorbing slime.
"When the hagfish is provoked, slime oozes from the hundred or so glands that line its body. The secretion swells in contact with sea water until it forms a slimy cocoon around the fish. The glands also secrete fine fibers that reinforce the slime and allow it to stretch without breaking. Each thread is more than 2 inches (50 cm) long, but the hagfish employs a neat method to prevent tangling - the threads are played out from the glands in winding layers, like a nautical rope stacked into a figure eight." (Downer 2002:104-105)
Learn more about this functional adaptation.