The Cetomimiformes or whalefishes are an order of small, deep-sea

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...

. Some authoritiesE.g. Nelson (2006) include the whalefishes as part of the order

Stephanoberyciformes The Stephanoberyciformes are an order of marine ray-finned fishes, consisting of about 68 species, the majority (61) of which belong to the ridgehead family (Melamphaidae). The Stephanoberyciformes are mostly uncommon deep-sea species with little ...

, within the

superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...

Cetomimoidea. Their sister order, the

Beryciformes The Beryciformes are a poorly-understood order of carnivorous ray-finned fishes consisting of 7 families, 30 genera, and 161 species. They feed on small fish and invertebrates. Beyond this, little is known about the biology of most member specie ...

, includes the flashlight fish and

squirrelfish Holocentrinae is a subfamily of Holocentridae containing 40 recognized species and one proposed species. Its members are typically known as squirrelfish and all are nocturnal. All three genera in the subfamily are found in the Atlantic and ''Ho ...

. Within this group are five families and approximately 18 genera and 32 species (but see below). Thought to have a circumglobal distribution throughout the tropical and temperate

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north po ...

s, whalefishes have been recorded at depths in excess of 3,500 metres.

Description

Named after their whale-shaped body (from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''ketos'' meaning "whale" or "sea monster", ''mimos'' meaning "imitative" and the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...

''forma'' meaning "form"), the Cetomimiformes have extremely large mouths and highly distensible stomachs. Their eyes are very small or vestigial; the lateral line (composed of huge, hollow tubes) is consequently very well developed to compensate for life in the pitch black depths. The dorsal and

anal fins Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...

are set far back; all fins lack spines. The

swim bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their current water depth w ...

is also absent, except in the

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. Th ...

e and juveniles which occur in the surface waters.Paxton ''et al.'' (2001) Whalefish coloration is typically red to orange, sometimes with a black body. Some species possess light-producing organs called

photophore A photophore is a glandular organ that appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors, h ...

s; these are widespread among deep-sea fishes. The largest known species reach a length of just 40 centimetres; most species are half this size.

Sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

is (apparently) exceptionally strong: males may only grow to 3.5 centimetres while females may be ten times as large. This is not uncommon among deep-sea fishes, with the males serving little use other than as suppliers of sperm: an even more extreme case are the

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...

males in deep-sea

anglerfish The anglerfish are fish of the teleost order Lophiiformes (). They are bony fish named for their characteristic mode of predation, in which a modified luminescent fin ray (the esca or illicium) acts as a lure for other fish. The luminescence ...

Families

Cetomimidae Cetomimidae is a family of small, deep-sea cetomimiform fish. They are among the most deep-living fish known, with some species recorded at depths in excess of . Adults are known as flabby whalefishes while juveniles are known as tapetails and ...

— flabby whalefishes *

Rondeletiidae The redmouth whalefishes are two species of deep-sea whalefishes in the genus ''Rondeletia'', the only genus in the family Rondeletiidae. They are apparently close to the velvet whalefish (''Barbourisia rufa''), and apparently also to the gibber ...

— redmouth whalefishes * Barbourisiidae — velvet whalefish (

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

) The gibberfishes (

Gibberichthyidae The Gibberichthyidae, also known as gibberfishes, are a small family of deep sea stephanoberyciform fish, containing a single genus, ''Gibberichthys'' (from the Latin ''gibba'', "humpbacked" and the Greek ''ichthys'', "fish"), and two species. ...

) on the other hand, usually placed in the

''sensu stricto'', appear to be close relatives of the

and Barbourisiidae, as has been occasionally proposed.Paxton ''et al.'' (2001)

Footnotes

References

* (2006): ''

Fishes of the World ''Fishes of the World'' by the American Ichthyology, ichthyologist Joseph S. Nelson (1937–2011) is a standard reference for fish systematics. Now in its fifth edition (2016), the work is a comprehensive overview of the diversity and classificat ...

'' (4th ed.). * (2001): Larvae and juveniles of the deepsea "whalefishes" ''Barbourisia'' and ''Rondeletia'' (Stephanoberyciformes: Barbourisiidae, Rondeletiidae), with comments on family relationships. ''Records of the Australian Museum'' 53(3): 407-425
PDF fulltext

External links

Whalefish - Smithsonian Ocean Portal
*
Aquatic community website
{{Taxonbar, from=Q859840 Ray-finned fish orders