Cetomimiformes
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Cetomimidae |
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.
Within the Cetomimiformes are five families and approximately 18 genera. Thought to have a circumglobal distribution throughout the tropical and temperate latitudes, whalefishes have been recorded at depths in excess of 3,500 metres. Their sister order, the Beryciformes, includes the flashlight fish and squirrelfish.
Named after their whale-shaped body (from the Greek 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 head; all fins lack spines. The swim bladder is also absent. Whalefish coloration is typically red to orange with a black body. Some species possess light-producing organs called photophores; these are typical of 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 could be said typical of deep-sea fishes, where the males serve little use other than as suppliers of sperm. A similar gender-to-size ratio is seen in deep-sea anglerfish.
Order Cetomimiformes
Families
- Cetomimidae - Flabby whalefishes
- Rondeletiidae - Redmouth whalefishes
- Barbourisiidae - Velvet whalefish (monotypic)
- Megalomycteridae - Largenose fishes
- Mirapinnidae - Hairyfish and tapetails (or ribbonbearers)