Longneck eels or neck eels are a family, Derichthyidae, of eel

Eel

Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...

s. They are pelagic fish

Pelagic fish

Pelagic fish live near the surface or in the water column of coastal, ocean and lake waters, but not on the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and reef fish which are associated with coral reefs.The marine pelagic...

es, found in the middle and depths of most oceans. The name comes from Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 deres meaning "neck" and ichthys meaning "fish".

They are distinguished by the presence of a series stripes on the head that form part of the sensory system, but otherwise the two genera of the family are quite different in appearance. Derichthys has a narrow neck and large eyes, while Nessorhamphus has a long, flattened, snout. They grow to about 60 centimetres (23.6 in) in length.

Species

There are three species in two genera:

• Genus Derichthys (1 species)
• Genus Nessorhamphus
  Nessorhamphus
  Nessorhamphus is a genus of eels in the family Derichthyidae. It currently contains the following species:* Nessorhamphus danae E. J. Schmidt, 1931...
  
  (2 species)

In some classifications (for example, Systema Naturae 2000) this family is split in two, with Derichthyidae containing only the genus Derichthys, and Nessorhamphus being assigned its own family, Nessorhamphidae.