Body compressed and elevated, covered with scales, either finely ctenoid or smooth. Lateral line continuous, not continued over the caudal fin. Mouth in front of the snout, generally small, with lateral cleft. Eye lateral, of moderate size. Six or seven branchiostegals. Teeth villiform or setiform, in bands, without canines or incisors. Dorsal fin consisting of a spinous and soft portion of nearly equal development; anal with three or four spines, similarly developed as the soft dorsal, both being many-rayed. The vertical fins more or less densely covered with small scales. The lower rays of the pectoral fin branched, not enlarged; ventrals thoracic, with one spine and five soft rays. Stomach coecal.
The typical forms of this family are readily recognised by the form of their body, and by a peculiarity from which they derive their name Squamipinnes; the soft, and frequently also the spinous part of their dorsal and anal fins are so thickly covered with scales that the boundary between fins and body is entirely obliterated. The majority are inhabitants of the tropical seas, and abound chiefly in the neighbourhood of coral-reefs. The beauty and singularity of distribution of the colours of some of the genera, as Chætodon, Heniochus, Holacanthus, is scarcely surpassed by any other group of fishes. They remain within small dimensions, and comparatively few are used as food. They are carnivorous, feeding on small invertebrates. Only a few species enter brackish water.
Extinct representatives of this family are not scarce at Monte Bolca and in other tertiary formations. All, at least those admitting of definite determination, belong to existing genera, viz. Holacanthus, Pomacanthus, Ephippium, Scatophagus. Very singular is the occurrence of Toxotes in the Monte Bolca strata.
The following genera have no teeth on the palate:—
Chætodon.—One dorsal fin, without any notch in its upper margin, and with the soft and spinous portions similarly developed; none of the spines elongate. Snout short or of moderate length. Præoperculum without, or with a fine, serration, and without spine at the angle. Scales generally large or of moderate size.
Fig. 167.—Chætodon ephippium.
Seventy species are known from the tropical parts of the Atlantic and Indo-Pacific, nearly all being beautifully ornamented with bands or spots. Of the ornamental markings a dark or bicoloured band, passing through the eye and ascending towards the back, is very generally found in these fishes; it frequently occurs again in other marine Acanthopterygians, in which it is not rarely a sign of the immature condition of the individual. The Chætodonts are most numerous in the neighbourhood of the coral-reefs of the Indo-Pacific, the species figured (C. ephippium) being as common in the East Indian Archipelago as in Polynesia, like many others of its congeners.
Chelmo differs from Chætodon only in having the snout produced into a more or less long tube.
