An order of about 219 species of teleost fishes ranked in four suborders. The order is distinguished by certain skeletal specializations of the gill arches that are unknown in other teleost fishes. They share characters with the order Myctophiformes (lanternfishes) to the extent that they are combined under the ordinal name Myctophiformes by some authors. In both orders the premaxilla excludes the maxilla from the gape of the mouth; the mouth is not protractile; an adipose fin is usually present; the caudal fin is forked; pelvic fins are usually abdominal; light-producing organs are often present; a swim bladder, if present, is physoclistous (not connected to the gut); and some families have hermaphroditic species with self-fertilization.