The Cetomimoidea or whalefishes are a
superfamily of small, deep-sea
ray-finned fish. Formerly treated as either their own order (Cetomimiformes) due to their unusual anatomy, more recent studies incorporating genetic data confirm them to be deeply nested within the
Beryciformes as a clade within
Stephanoberycoidei (which was formerly also treated as its own order).
They are thus better treated as their own superfamily, Cetomimoidea.
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
latitudes, whalefishes have been recorded at depths in excess of 3,500 metres.
Taxonomy
Some recent phylogenetic studies suggest that the whalefishes are paraphyletic with respect to other members of the suborder, with ''
Barbourisia'' belonging to the
Stephanoberycidae while
Rondeletiidae includes ''
Hispidoberyx''. Although previously thought to have ancient origins due to their unique morphological characteristics, phylogenetic studies suggest a
Paleogene origin for the group.
Potentially the earliest fossil record of the group is of a ''
Rondeletia''-like whalefish from the earliest Eocene-aged
Fur Formation of Denmark.
Description
Named after their whale-shaped body (from the
Greek ''ketos'' meaning "whale" or "sea monster", ''mimos'' meaning "imitative" and the
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
''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 are set far back; all fins lack spines. The
swim bladder is also absent, except in the
larvae 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
photophores; 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 sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...
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 males in deep-sea
anglerfish.
Families
*
Cetomimidae — flabby whalefishes
*
Rondeletiidae — 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 "unisp ...
)
The gibberfishes (
Gibberichthyidae) on the other hand, usually placed in the
Stephanoberyciformes ''sensu stricto'', appear to be close relatives of the
Rondeletiidae and
Barbourisiidae, as has been occasionally proposed.
[Paxton ''et al.'' (2001)]
Footnotes
References
* (2006): ''
Fishes of the World'' (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
Beryciformes