''Pseudocetonurus septifer'' is a species of

rattail Grenadiers or rattails are generally large, brown to black gadiform marine fish of the subfamily Macrourinae, the largest subfamily of the family Macrouridae. Found at great depths from the Arctic to Antarctic, members of this subfamily are am ...

, the only known species in the genus ''Pseudocetonurus''. This fish is found at depths of up to 950 m in the waters around

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

and in the south-eastern

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

. It has recently also been recorded on the other side of the Pacific, near

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...

, and this species probably has a pan-Pacific distribution but has been underrecorded due to the depths in which it lives. This species attains a length of up to 39 cm. It is unique among rattails in having 7 branchiostegal rays and a large

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

opening. This is a generally very dark, sometimes black, fish with a very large head and small, widely spaced eyes. There is a small

bioluminescent Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorganisms including ...

organ located between the

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two en ...

References

A new species, ''Caelorinchus sheni'', and 19 new records of grenadiers (Pisces: Gadiformes: Macrouridae) from Taiwan - CHIOU Mei-Luen ; SHAO Kwang-Tsao ; IWAMOTO Tomio
Macrouridae Monotypic fish genera Fish described in 1982 Fish of the Pacific Ocean {{Gadiformes-stub