Cetomimiformes
Encyclopedia
The Cetomimiformes or whalefishes are an order of small, deep-sea ray-finned fish. Some authorities include the whalefishes as part of the order Stephanoberyciformes
, within the superfamily
Cetomimoidea. Their sister order, the Beryciformes
, includes the flashlight fish
and squirrelfish.
Within this group are five families and approximately 18 genera (but see below). Thought to have a circumglobal distribution throughout the tropical and temperate latitude
s, whalefishes have been recorded at depths in excess of 3,500 metres.
ketos meaning "whale" or "sea monster", mimos meaning "imitative" and the Latin
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 of the penis; all fins lack spines. The swim bladder is also absent, except in the larva
e and juveniles
which occur in the surface waters. Whalefish coloration is typically red to orange, sometimes with a black body. Some species possess light-producing organs called photophore
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
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
.
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.
Stephanoberyciformes
The Stephanoberyciformes are an order of marine ray-finned fishes, consisting of about 45 species, the majority of which belong to the ridgehead family . The Stephanoberyciformes are mostly uncommon deep-sea species with little, if any, importance to commercial fishery...
, within the superfamily
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
Cetomimoidea. Their sister order, the Beryciformes
Beryciformes
Beryciformes is an order of ray-finned fishes. This is a very poorly understood group of 16 families, 57 genera, and about 219 species. Some people believe that it is probably an artificial assemblage of unrelated taxa that are thrown together for convenience only; there are no convincing...
, includes the flashlight fish
Flashlight fish
The flashlight fish are a family, the Anomalopidae, of beryciform fish. There are some unrelated fish with similar features, some of which are also called flashlight fish. Notable among these are the deep sea lanternfish, of the family Myctophidae, of which there are over 200 species.Flashlight...
and squirrelfish.
Within this group are five families and approximately 18 genera (but see below). Thought to have a circumglobal distribution throughout the tropical and temperate latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
s, whalefishes have been recorded at depths in excess of 3,500 metres.
Description
Named after their whale-shaped body (from the GreekGreek 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;...
ketos meaning "whale" or "sea monster", mimos meaning "imitative" and the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
forma meaning "form"), the Cetomimiformes have extremely large mouths and highly distensible stomachs. Their eyes are very small or vestigial; the lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
(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 of the penis; all fins lack spines. The swim bladder is also absent, except in the larva
Larva
A larva 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...
e and juveniles
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
which occur in the surface waters. Whalefish coloration is typically red to orange, sometimes with a black body. Some species possess light-producing organs called photophore
Photophore
A photophore is a light-emitting organ which 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...
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
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
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
Anglerfish
Anglerfishes are members of the teleost order Lophiiformes . They are bony fishes named for their characteristic mode of predation, wherein a fleshy growth from the fish's head acts as a lure; this is considered analogous to angling.Some anglerfishes are pelagic , while others are benthic...
.
Families
- Cetomimidae — flabby whalefishes
- Rondeletiidae — redmouth whalefishes
- Barbourisiidae — Velvet Whalefish (monotypicMonotypicIn biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
)
The gibberfishes (Gibberichthyidae
Gibberichthyidae
Gibberichthyidae, also known as Gibberfishes, are a type of living, vertebrata fish. This fish carries an IUCN Red List status of "Not Evaluated".-References:*http://www.discoverlife.org/mp/20q?search=Gibberichthyidae*http://www.eol.org/pages/5082...
) on the other hand, usually placed in the Stephanoberyciformes
Stephanoberyciformes
The Stephanoberyciformes are an order of marine ray-finned fishes, consisting of about 45 species, the majority of which belong to the ridgehead family . The Stephanoberyciformes are mostly uncommon deep-sea species with little, if any, importance to commercial fishery...
sensu stricto, appear to be close relatives of the Rondeletiidae and Barbourisiidae, as has been occasionally proposed.