''Stylephorus chordatus'', the tube-eye or thread-tail, is a deep-sea 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 long, its pair of tail fin rays triple its length to about . Its eyes are tubular in shape, resembling a pair of binoculars. It has a tubular mouth through which it sucks seawater by enlarging its oral cavity to about 40 times its original size. It then expels the water through the gills, leaving behind the

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s on which it feeds. The phylogenetic position of the tube-eye has been controversial. It has been historically placed amongst Lampriformes, but a study involving

mitochondrial A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is use ...

and nuclear DNA sequences analysis suggested ''Stylephorus'' is instead a close parent of the Gadiformes order (cods and hakes).

References

Stylephoridae Monotypic fish genera Fish described in 1791 {{Paracanthopterygii-stub