The tube-eye or thread-tail, Stylephorus chordatus, is a deep-sea Lampriformes fish, the only fish in the genus Stylephorus and family Stylephoridae.

It is found in deep subtropical and tropical waters around the world, living at depths during the day and making nightly vertical migrations to feed on plankton. It is an extremely elongated fish; although its body grows only to 28 cm (11 in) long, its pair of tail fin rays triple its length to about 90 cm (35 in). Its eyes are tubular in shape, resembling a pair of binoculars.