Fig. 337.—Spadefish, Chætodipterus faber (L.). Virginia.
The Platacidæ.—Closely related to the Ilarchidæ is also the East Indian family of Platacidæ, remarkable for the very great depth and compression of the body, which is much deeper than long, and the highly elevated dorsal and anal still further emphasize this peculiarity of form. In this group the few dorsal spines are closely attached to the soft rays and the general color is dusky. In the young the body is deeper than in the adult and the ventral fins much more produced. The best-known species is the tsuzume or batfish (Platax orbicularis), which ranges from India through the warm current to northern Japan. Platax teira, farther south, is very similar. Platax altissimus, with a very high dorsal, is a fossil in the Eocene of Monte Bolca.
Fig. 338.—Butterfly-fish, Chætodon capistratus Linnæus. Jamaica.
The Butterfly-fishes: Chætodontidæ.—The central family of Squamipinnes is that of the butterfly-fishes or Chætodontidæ. In this group the teeth are distinctly brush-like, the mouth small, the dorsal fin continuous and closely scaly, and the ventral fins with one spine and five rays. The species are mostly of small size and brilliant and varied coloration, yellow and black being the leading colors. They vary considerably with age, the young having the posterior free edges of the bones of the head produced, forming a sort of collar. These forms have received the name of Tholichthys, but that supposed genus is merely the young of Chætodon. The species of Chætodontidæ abound in rock pools and about coral reefs in clear water. They are among the most characteristic forms of these waters and their excessive quickness of movement compensates for their conspicuous coloration. In these confined localities they have, however, few enemies. The broad bodies and spinous fins make them rather difficult for a large fish to swallow. They feed on small crustaceans, worms, and the like. The analogy to the butterfly is a striking one, giving rise to the English name, butterfly-fish, the Spanish mariposa, and the Japanese chochouwo, all having the same meaning. Fossil chætodonts are rather few, Chætodon pseudorhombus of the Pliocene of France, Holocanthus microcephalus and Pomacanthus subarcuatus of the Eocene, being the only species recorded by Zittel.
Fig. 339.—Black Angel-fish, Pomacanthus arcuatus (Linnæus). Barnegat, New Jersey.
In the principal genus, Chætodon, the colors are especially bright. There is almost always a black bar across the eye, and often black ocelli adorn the fins. This genus is wanting in Europe. Chætodon capistratus, striatus, and numerous other species are found in the West Indies; Chætodon humeralis and nigrirostris are common on the coast of Mexico. The center of their distribution is in Polynesia and the East Indian Archipelago. Chætodon reticulatus, lineolatus, ulietensis, ornatissimus, ephippion, setifer, and auriga are among the most showy species. Numerous closely related genera are described. In some of these the snout is prolonged into a long tube, bearing the jaws at its end. Of this type are Chelmo in India, Forcipiger in Polynesia, and Prognathodes in the West Indies. Heniochus (macrolepidotus) has one dorsal spine greatly elongated. Microcanthus strigatus, one of the most widely distributed species, is known by its small scales. Megaprotodon (triangularis) has four anal spines instead of three as in the others.
Fig. 340.—Angel-fish or Isabelita, Holacanthus ciliaris (Linnæus). Jamaica. Family Chætodontidæ.