# Natural History, Fishes/Plectognathi

ORDER III. PLECTOGNATHI.
(Fishes with soldered jaws.)
The skeleton in this Order is partly bony in texture, and partly cartilaginous, presenting a decided approach to the following group, in which the gristly structure wholly prevails. The ribs are present only as mere vestiges: the jaws are formed by the union (or soldering together, if we may so speak,) of the maxillary and inter-maxillary bones, and the arch of the palate is united to the skull, so as to be deprived of independent motion. Hence the mouth in these fishes is small, powerless, and almost motionless. The gill-covers and gill-rays are imperfectly developed; and are concealed under the thick skin, leaving only a small orifice for the escape of the water from the gills. The body is destitute of true scales; the skin is either hard and leathery, and scored into lozenge-shaped divisions, or covered with hard bony spines, or soft and mucous. The form is usually short and thick, sometimes quite destitute of the proportions that we are accustomed to see in other fishes, and, as it were, deformed: the fins are commonly small, and often remarkable for their position or structure; there are no proper ventrals.
The Order before us is very limited in extent as compared with the others; the fishes which compose it, though presenting some curious ​points of structure and economy, and therefore not without interest to the naturalist, are of little value; their flesh being in general rank and glutinous, and unfit for human food. Most of the species are natives of the tropical seas; though an individual occasionally strays into colder climates. We shall consider them as forming two Families, Tetraodontidæ and Balistidæ.
Family I. Tetraodontidæ.
(Naked-toothed Fishes.)
Instead of teeth arranged in some sort of serried order, the fishes before us have them united into masses, presenting externally no trace of individuality, but internally showing a number of parallel thin plates. The form of these masses of teeth resembles that of a parrot’s beak, and they are covered with a common coat of ivory-like substance. They are continually renewed by the growth of the component plates, as the surfaces are worn down by grinding the sea-weeds and crustaceous animals that constitute the common food of the Family.
Most of the species have the skin covered with prickles, differing in number and strength, and capable of being erected. They are, in general, endowed with the power of inflating the body with air to a remarkable degree. One genus, that of the Sun-fishes (Orthagoriscus), is destitute of both these characters; but it is marked by an equally curious peculiarity of form: the tail being so short, and the posterior termination ​of the body so abrupt, that the observer is apt to imagine that he looks upon the anterior half of a fish, cut across through its middle. These are fishes of gigantic size, which are sometimes taken in the British seas.
About a hundred species are enumerated as belonging to the Family, the great majority of which are confined to the warm parts of the ocean. All are, we believe, marine in their habits.
Genus Tetraodon. (Linn.)
A depressed line, passing down the front of the aggregated teeth in both jaws, gives to the fishes of this genus the appearance of possessing four great teeth, two above and two below, whence the generic appellation. The body, either wholly or at least on the under parts, is studded with prickles, varying in size and in number. In some species, indeed, these are so small and so imbedded in the soft mucous skin, as not to be perceptible in a living state, but drying or preservation in spirit reveals them.
“The species of this genus,” observes Dr. Roget, “are remarkable for being provided with the means of suddenly assuming a globular form by swallowing air, which passing into the crop or first stomach, blows up the whole animal like a balloon. The abdominal region being thus rendered the lightest, the body turns over, the stomach being the uppermost part, and the fish floats upon its back, without having the power of directing itself during the state of forced distension. But it is while thus bloated and ​passive, at the mercy of the waves, that this animal is really most secure; for the numerous spines with which the surface of the body is universally beset are raised and erected by the stretching out of the skin, thus presenting an armed front to the enemy on whatever side he may venture to begin the attack.”
Specimens of a species called Pennant's Globe-fish (Tetraodon Pennantii Yarr.) are
occasionally taken on the coast of Cornwall. It is about a foot and a half in length; of a rich blue colour on the superior parts, and silvery white on the sides and belly, studded all over the last-named part, which is capable of inflation, with clusters of spines, each group consisting of four radiating from a centre.
Family II. Balistidæ. (File-fishes.)
In this Family the muzzle from the eyes onward is conical, or pyramidal in form, terminating in a small mouth, with distinct teeth in both jaws. The skin is either rough and marked with lines or scorings crossing each other at definite angles, or else covered with angular bony plates. The air-bladder is large, strong and oval. There are one hundred and ten species known, all natives of the warmer seas; and they form two Sub-families.
1. Balistina. The File-fishes. In these the body is compressed, more or less oval, and covered with a granulated, hard, leathery skin, marked all over with a scored pattern of lozenges, the crossing lines being perfectly smooth, while the rest of the skin is rough. They have eight teeth in one row in each jaw.
2. Ostracionina. The Trunk-fishes. These have the body angular, four or three-sided, covered with angular plates of solid bone soldered together, and forming a sort of inflexible box, with openings for the mouth, the fins, the tail, and the gill-aperture. They have ten or twelve conical teeth in each jaw.
Genus Balistes. Linn.)
The body, which generally assumes an oval form, more or less pointed at each end, and often compressed, is invested with a leathery skin, ​covered with minute rough points, except in regular lines which cross each other, and mark off the whole surface into lozenge-shaped divisions. The appearance is so much like that of a smith's rasp or file, as to have suggested the name of File-fish, by which the genus is commonly known. There are two dorsals, of which the first is composed of three spinous rays. The ventrals have each a strong bony spine, without membranes; the other fins are generally much developed. In some species the sides of the tail are armed with rows of sharp prickles.
The first ray of the front dorsal is a strong pointed bone, studded along its anterior side with hard rough points. It is a powerful weapon, the effect of which is heightened by an interesting contrivance. When it is erected, which is effected with a kind of spring or catch, no force can depress it, but the least touch applied to the second or third, lowers the whole fin in a moment. Hence it is named Balistes, from the ancient machine which shot darts at an enemy. The structure by which this effect is produced is thus explained by Professor Owen. "The first spine is articulated by a very remarkable joint to [a broad bony plate on the top of the head]; its base is expanded and perforated, and a bony bolt passes freely through the ring. When this spine is raised, a depression at the back part of its base receives a corresponding projection from the contiguous base of the second ray, which fixes it like the hammer of the gun-lock at full cock; and it cannot be forced down till the small spine has been depressed, as by pulling the trigger: it is then received into a groove on the ​supporting plate, and offers no impediment to the progress of the fish through the water."
These fishes are generally adorned with rich and brilliant colours, often arranged in diagonal lines or bands; they abound in the seas of hot climates, generally swimming among the rocks, like the Chætodons, which they not a little resemble. Some have the body set with curiously branched filaments. Their flesh is rank and unwholesome.
We illustrate the genus by a description and figure of Balistes velatus (Bloch.), a West
Indian species which has fallen under our observation. The dorsal and each lobe of the caudal are produced into long pointed filaments. The body is purplish brown on the upper parts, with the throat and belly pale buff. Several curved lines and bands pass across the face, of a rich azure hue, with yellow edges. The fins are blackish purple.
* ↑ Bridgewater Treat. i. 433.
* ↑ Comp. Anat. ii. 69.