The Porcupine-fishes: Diodontidæ.—In the remaining families of Gymnodontes, there is no suture in either jaw, the teeth forming an undivided beak. The Diodontidæ, or porcupine-fishes, have the body spherical or squarish, and armed with sharp thorns, the bases of which are so broad as to form a continuous coat of mail. In some of them, part of the spines are movable, these being usually two-rooted; in others, all are immovable and three-rooted. All are reputed poisonous, especially in the equatorial seas.
In Diodon the spines are very long, the anterior ones, at least, movable. The common porcupine-fish, Diodon hystrix, is found in all seas, and often in abundance. It is a sluggish fish, olive and spotted with black. It reaches a length of two feet or more, and by its long spines it is thoroughly protected from all enemies. A second species, equally common, is the lesser porcupine-fish, Diodon holacanthus. In this species, the frontal spines are longer than those behind the pectoral, instead of the reverse, as in Diodon hystrix. Many species of Diodon are recorded from the Eocene, besides numerous species from later deposits. One of these, as Heptadiodon heptadiodon from the Eocene of Italy, with the teeth subdivided, possibly represents a distinct family. Diodon erinaceus is found in the Eocene of Monte Bolca and Progymnodon hilgendorfi in the Eocene of Egypt.
Fig. 362.—Rabbit-fish, Chilomycterus schœpfi (Walbaum). Noank, Conn.
In the rabbit-fishes (Chilomycterus) the body is box-shaped, covered with triangular spines, much shorter and broader at base than those of Diodon. Numerous species are known.
Chilomycterus schœpfi is the common rabbit-fish, or swell-toad of our Atlantic coast, light green, prettily varied with black lines. The larger, Chilomycterus affinis, with the pectoral fin spotted with black, is widely diffused through the Pacific. It is rather common in Japan, where it is the torabuku, or tiger puffer. It is found also in Hawaii, and it is once recorded by Dr. Eigenmann from San Pedro, California, and once by Snodgrass and Heller, from the Galapagos.
The Head-fishes: Molidæ.—The headfishes, or Molidæ, also called sunfishes, have the body abbreviated behind so that the dorsal, anal, and caudal fins seem to be attached to the posterior outline of the head. This feature, constituting the so-called gephyrocercal tail is a trait of specialized degradation.
Fig. 363.—Headfish (adult), Mola mola (Linnæus). Virginia.
Mola mola, the common head-fish or sunfish, is found occasionally in all tropical and temperate seas. Its form is almost circular, having been compared by Linnæus to a mill-wheel (mola), and its surface is covered with a rough, leathery skin. It swims very lazily at the surface of the water, its high dorsal often rising above the surface. It is rarely used as food, though not known to be poisonous. The largest example known to the writer was taken at Redondo Beach, California, by Mr. Thomas Shooter, of Los Angeles. This specimen was 8 feet 2 inches in length, and weighed 1200 pounds. Another, almost as large, was taken at San Diego, in April, 1904. No difference has been noticed among specimens from California, Cape Cod, Japan, and the Mediterranean. The young, however, differ considerably from the adult, as might be expected in a fish of such great size and extraordinary form. (See Figs. 109 and 110, Vol. I.)