B.—Teleostei.—Plectognathi.
The Order Plectognathi (Family Gymnodontes) includes the genera Diodon, Tetrodon and Triodon, globular fishes, in which the jaw is transformed into a beak and furnished with a sharp dentary plate. Their œsophagus is dilated into a resonant air-pouch. When removed from the water they swallow air and dilate the pouch, and the expulsion of this air is accompanied by a loud noise.
Several species of Tetrodon are armed with spines, which produce very painful wounds. Their flesh is toxic, but it has not been proved that poison-glands exist at the base of the spines.
On the shores of the Cape of Good Hope, Brazil, China, and Japan these fishes are much feared. The principal species are Tetrodon stellatus (Indian and Pacific Oceans; [fig. 115]) and T. rubripes (Japan; [fig. 116]).
Fig. 115.—Tetrodon stellatus (Indian and Pacific Oceans). (After Savtschenko.)
Fig. 116.—Tetrodon rubripes (Japan). (After Savtschenko.)
Closely allied to Diodon, and feared like the foregoing on account of their spines, which are sometimes scattered all over the body, are the species of the genus Chilomycterus, the most important of which are C. orbicularis ([fig. 117]), and C. tigrinus ([fig. 118]), both of which are found in the Indian Ocean.
Fig. 117.—Chilomycterus orbicularis (Indian Ocean). (After Savtschenko.)
Fig. 118.—Chilomycterus tigrinus (Indian Ocean). (After Savtschenko.)