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Tetraodontiformes

(Order)

Overview

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The Tetraodontiformes are an order of highly derived ray-finned fish, also called the Plectognathi. Sometimes these are classified as a suborder of the Perciformes. The Tetraodontiformes are represented by ten families and approximately 360 species overall; most are marine and dwell in and around tropical coral reefs, but a handful of species are found in freshwater streams and estuaries. They have no close relatives, and descend from a line of coral-dwelling species that emerged around 40 million years ago.

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Various bizarre forms are included here, all radical departures from the streamlined body plan typical of most fishes. These forms range from nearly square or triangular (boxfishes), globose (pufferfishes) to laterally compressed (filefishes) and triggerfish. They range in size from Rudarius excelsus, measuring just 2 centimetres (0.79 in) in length, to the ocean sunfish, the largest of all bony f ish at up to 3 metres (9.8 ft) in length and weighing over 2 tonnes.[1]

Most members of this order, except for the Balistidae family, are ostraciiforms, meaning the body is rigid and incapable of lateral flexure. Because of this, they are slow-moving and rely on their pectoral, dorsal, anal, and caudal fins for propulsion rather than by body undulation. However, movement is usually quite precise; dorsal and anal fins aid in manoeuvring and stabilizing. In most species, all fins are simple, small, and rounded, except for the pelvic fins which, if present, are fused and buried. Again, in most members, the gill plates are covered over with skin, the only gill opening a small slit above the pectoral fin.

The tetraodontiform strategy seems to be defense at the expense of speed, with all species fortified with scales modified into strong plates or spines ? or with tough, leathery skin (the filefishes and ocean sunfish). Another striking defensive attribute found in the pufferfishes and porcupinefishes is the ability to inflate the body to greatly increase its normal diameter: this is accomplished by sucking water into a diverticulum of the stomach. Many species of the Tetraodontidae, Triodontidae and Diodontidae are further protected from predation by tetrodotoxin, a powerful neurotoxin concentrated in the animals' internal organs.

Long-spine porcupinefish, Diodon holocanthus. On the right is a blue-spotted grouper, Cephalopholis argus.

Tetraodontiforms have highly modified skeletons, with no nasal, parietal, infraorbital, or (usually) lower rib bones. The bones of the jaw are modified and fused into a sort of "beak"; there are visible sutures which divide the beaks into "teeth". This is alluded to in their name, derived from the Greek words tetra meaning "four" and odous meaning "tooth" and the Latin forma meaning "shape". Counting these teeth-like bones is a way of distinguishing similar families. For example the Tetraodontidae ("four-toothed"), Triodontidae ("three-toothed"), and Diodontidae ("two-toothed").

The jaws are aided by powerful muscles and many species also have pharyngeal teeth to further process prey items. This is because Tetraodontiformes prey mostly on hard-shelled invertebrates such as crustaceans and shellfish.

The Molidae are conspicuous even within this oddball order: they lack swim bladders and spines, and are propelled by their very tall dorsal and anal fins. The caudal peduncle is absent and the caudal fin is reduced to a stiff rudder-like structure. Molids are pelagic rather than reef-associated and feed on soft-bodied invertebrates, especially jellyfish.

Families

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Ocean sunfish.
The Honeycomb cowfish is part of the Ostraciidae family.

Fossil families

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Timeline of genera

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atives, and descend from a line of coral-dwelling species that emerged around 40 million years ago.

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Various bizarre forms are included here, all radical departures from the streamlined body plan typical of most fishes. These forms range from nearly square or triangular (boxfishes), globose (pufferfishes) to laterally compressed (filefishes) and triggerfish. They range in size from Rudarius excelsus, measuring just 2 centimetres (0.79 in) in length, to the ocean sunfish, the largest of all bony fish at up to 3 metres (9.8 ft) in length and weighing over 2 tonnes.[1]

Most members of this order, except for the Balistidae family, are ostraciiforms, meaning the body is rigid and incapable of lateral flexure. Because of this, they are slow-moving and rely on their pectoral, dorsal, anal, and caudal fins for propulsion rather than by body undulation. However, movement is usually quite precise; dorsal and anal fins aid in manoeuvring and stabilizing. In most species, all fins are simple, small, and rounded, except for the pelvic fins which, if present, are fused and buried. Again, in most members, the gill plates are covered over with skin, the only gill opening a small slit above the pectoral fin.

The tetraodontiform strategy seems to be defense at the expense of speed, with all species fortified with scales modified into strong plates or spines ? or with tough, leathery skin (the filefishes and ocean sunfish). Another striking defensive attribute found in the pufferfishes and porcupinefishes is the ability to inflate the body to greatly increase its normal diameter: this is accomplished by sucking water into a diverticulum of the stomach. Many species of the Tetraodontidae, Triodontidae and Diodontidae are further protected from predation by tetrodotoxin, a powerful neurotoxin concentrated in the animals' internal organs.

Long-spine porcupinefish, Diodon holocanthus. On the right is a blue-spotted grouper, Cephalopholis argus.

Tetraodontiforms have highly modified skeletons, with no nasal, parietal, infraorbital, or (usually) lower rib bones. The bones of the jaw are modified and fused into a sort of "beak"; there are visible sutures which divide the beaks into "teeth". This is alluded to in their name, derived from the Greek words tetra meaning "four" and odous meaning "tooth" and the Latin forma meaning "shape". Counting these teeth-like bones is a way of distinguishing similar families. For example the Tetraodontidae ("four-toothed"), Triodontidae ("three-toothed"), and Diodontidae ("two-toothed").

The jaws are aided by powerful muscles and many species also have pharyngeal teeth to further process prey items. This is because Tetraodontiformes prey mostly on hard-shelled invertebrates such as crustaceans and shellfish.

The Molidae are conspicuous even within this oddball order: they lack swim bladders and spines, and are propelled by their very tall dorsal and anal fins. The caudal peduncle is absent and the caudal fin is reduced to a stiff rudder-like structure. Molids are pelagic rather than reef-associated and feed on soft-bodied invertebrates, especially jellyfish.

Families

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Ocean sunfish.
The Honeycomb cowfish is part of the Ostraciidae family.

Fossil families

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Timeline of gen era

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References

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  1. ^ a b Keiichi, Matsura & Tyler, James C. (1998). Paxton, J.R. & Eschmeyer, W.N.. ed. Encyclopedia of Fishes. San Diego: Academic Press. pp. 230. ISBN 0-12-547665-5. 

Taxonomy

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The Order Tetraodontiformes is further organized into finer groupings including:

Families

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Aracanidae

The Aracanidae are a family of bony fishes related to the boxfishes. They are somewhat more primitive than the true boxfishes, but have a similar protective covering of thickened scale plates. They are found in the Indian Ocean and the west Pacific. Unlike the true boxfishes, they inhabit deep waters, of over 200 metres (660 ft) in depth. [more]

Balistidae

Triggerfishes are about 40 species of often brightly colored fishes of the family Balistidae. Often marked by lines and spots, they inhabit tropical and subtropical oceans throughout the world, with the greatest species richness in the Indo-Pacific. Most are found in relatively shallow, coastal habitats, especially at coral reefs, but a few, such as the aptly named oceanic triggerfish (Canthidermis maculata), are pelagic. While several species from this family are popular in the marine aquarium trade, they are often notoriously ill-tempered. [more]

Cretatriacanthidae

[more]

Diodontidae

Porcupinefish are fish of the family Diodontidae, (order Tetraodontiformes), also commonly called blowfish (and, sometimes, "balloonfish" and "globefish"). [more]

Molidae

Molidae is the family of the molas or ocean sunfishes, unique fish whose bodies come to an end just behind the dorsal and anal fins, giving them a "half-a-fish" appearance. They are also the largest of the ray-finned bony fishes, with the ocean sunfish Mola mola recorded at up to 3.3 metres (11 ft) in length and 2 tonnes (2.2 short tons) in weight. [more]

Monacanthidae

Filefish (also known as foolfish, leatherjackets or shingles) are tropical to subtropical tetraodontiform marine fish of the diverse family Monacanthidae. Found in the Atlantic, Pacific and Indian Oceans, the filefish family contains approximately 107 species in 26 genera. Filefish are closely related to the triggerfish, pufferfish and trunkfish. [more]

Ostraciidae

Ostraciidae is a family of squared, bony fish belonging to the order Tetraodontiformes, closely related to the pufferfishes and filefishes. Fish in the family are known variously as boxfishes, cofferfishes, cowfishes and trunkfishes. It contains about 33 species in nine extant genera. [more]

Tetraodontidae

Tetraodontidae is a family of primarily marine and estuarine fish of the Tetraodontiformes order. The family includes many familiar species, which are variously called pufferfish, balloonfish, blowfish, bubblefish, globefish, swellfish, toadfish, toadies, honey toads, sugar toads, and sea squab. They are morphologically similar to the closely related porcupinefish, which have large external spines (unlike the thinner, hidden spines of Tetraodontidae, which are only visible when the fish has puffed up). The scientific name refers to the four large teeth, fused into an upper and lower plate, which are used for crushing the shells of crustaceans and mollusks, their natural prey. [more]

Triacanthidae

Triacanthidae, commonly known as triplespines or tripodfishes, is a family of Indo-Pacific fishes. It is classified in the order Tetraodontiformes, along with the pufferfishes and the ocean sunfish. The family consists of seven species in four genera, in addition to one extinct genus. [more]

Triacanthodidae

The spikefishes (family Triacanthodidae) are ray-finned fishes related to the pufferfishes and triggerfishes. They live in deep waters, below 50 metres (160 ft), but above the continental shelves. They are found in the Atlantic, Indian Ocean, and the west-central Pacific. [more]

Trigonodontidae

[more]

Triodontidae

The threetooth puffer, Triodon macropterus, is a tetraodontiform fish, the only living species in the genus Triodon and family Triodontidae. Other members of the family are known from fossils stretching back to the Eocene. [more]

More info about the Family Triodontidae may be found here.

References

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  1. ^ a b Keiichi, Matsura & Tyler, James C. (1998). Paxton, J.R. & Eschmeyer, W.N.. ed. Encyclopedia of Fishes. San Diego: Academic Press. pp. 230. ISBN 0-12-547665-5. 

Sources

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Last Revised: August 24, 2012
2012/08/24 13:15:28