Sea-horses swim with the body more or less vertical, the motive power being supplied by rapid vibration of the back-fin. Both pipe-fishes and sea-horses occur in British seas, the first being the more common.
Photo by H. V. Letkmann] [New York.
COFFER-FISHES.
Coffer-fishes have the body encased in a hard shell of closely fitting plates, leaving only the tail and fins free to move.
The Comb-gilled Fishes, to which we come next, are divided into two families, whose members are as remarkable for their extraordinary shape as are the tuft-gilled forms just discussed. The abnormal shapes which mark out certain fishes so conspicuously from the more normal and typical forms are generally regarded as adaptations, serving to ensure concealment, to ward off attack, or to effect the capture of prey otherwise unattainable. Instances illustrating all three of these ends are furnished by these two groups of the tuft- and comb-gilled fishes.
The File-fishes and Coffer-fishes, which form the first of the two families, present considerable variation in shape as well as in the covering of the body, which may be naked, covered with rough scales or bony spines, or invested in a complete bony cuirass.
The file-fishes are represented by numerous species, the typical one being known also as the Trigger-fish, on account of an armature of spines on the top of the back. These spines are three in number; the first is very strong, roughened like a file—hence the name File-fish—and hollowed out behind to receive the second much smaller spine, which has a projection in front at its base, fitting into a notch in the first. Thus these two spines can only be raised or depressed simultaneously, and the first cannot be forced down unless the second has been previously depressed. These fishes have very powerful teeth, to break off pieces of coral, which form a large part of their diet. They also destroy a large number of shell-fish, and work great destruction amongst pearl-oysters. Frequently these fishes, when eaten, prove highly poisonous, from having fed on poisonous corals, jelly-fish, or decomposing substances.
Photo by W. Saville-Kent, F.Z.S.] [Milford-on-Sea.