Trigla.—Head parallelopiped, with the upper surface and the sides entirely bony, the enlarged infraorbital covering the cheek.
Two dorsal fins. Three free pectoral rays. Villiform teeth. Air-bladder generally with lateral muscles, often divided into two lateral halves. The species may be referred to three groups:—
1. Palatine teeth none; scales exceedingly small, except those of the lateral line: Trigla.
2. Palatine teeth none; scales of moderate size: Lepidotrigla.
3. Palatine teeth present: Prionotus.
Fig. 214.—Trigla pleuracanthica.
Fig. 215.—Scute of the lateral line of the same fish.
About forty species of “Gurnards” are known from tropical and temperate zones. They are too well known to need detailed description; one of their principal characteristics is the three free finger-like pectoral appendages, which serve as organs of locomotion as well as touch, and which are supplied with strong nerves, as noticed above (pp. 108 and 120). The fins are frequently beautifully ornamented, especially the inner side of the long and broad pectorals, which is most exposed to the light when the fish is floating on the surface of the water, with pectorals spread out like wings. The grunting noise made by Gurnards when taken out of the water is caused by the escape of gas from the air-bladder through the open pneumatic duct. Gurnards are generally used as food; seven species occur on the British coast: the Red Gurnard (T. pini), the Streaked Gurnard (T. lineata), the Sapphirine Gurnard (T. hirundo), the Grey Gurnard (T. gurnardus), Bloch’s Gurnard (T. cuculus), the Piper (T. lyra), and the Long-finned Gurnard (T. obscura or T. lucerna). Singularly, the European species cross the Atlantic but rarely, the American species belonging chiefly to the division Prionotus.