Fig. 355.—Skeleton of the Cowfish, Lactophrys tricornis (Linnæus).
The Triodontidæ.—The most generalized family is that of the Triodontidæ. These fishes approach the Balistidæ in several regards, having the body compressed and covered with rough scales. The teeth form a single plate in the lower jaw, but are divided on the median line above. The compressed, fan-like, ventral flap is greatly distensible. Triodon bursarius, of the East Indies and northward to Japan, is the sole species of the family.
Fig. 356.—Silvery Puffer, Lagocephalus lævigatus (Linnæus). Virginia.
The Globefishes: Tetraodontidæ.—In the Tetraodontidæ (globefishes, or puffers), each jaw is divided by a median suture. The dorsal and anal are short, and the ventrals are reduced in number, usually fifteen to twenty (7 + 13 to 7 + 9). The walls of the belly are capable of extraordinary distension, so that when inflated, the fish appears like a globe with a beak and a short tail attached. The principal genus Spheroides contains a great variety of forms, forming a closely intergrading series. In some of these the body is smooth, in others more or less covered with prickles, usually three-rooted. In some the form is elongate, the color silvery, and the side of the belly with a conspicuous fold of skin. In these species, the caudal is lunate and the other fins falcate, and with numerous rays. But these forms (called Lagocephalus) pass by degrees into the short-bodied forms with small rounded fins, and no clear line has yet been drawn separating the group into genera. In these species each nostril has a double opening. Lagocephalus lagocephalus, large and silvery, is found in Europe. Lagocephalus lævigatus replaces it on the Atlantic Coast of North America. In Japan are numerous forms of this type, the venomous Lagocephalus sceleratus being one of the best known. Numerous other Japanese species, Spheroides xanthopterus, rubripes, pardalis, ocellatus, vermiculatus, chrysops, etc., mark the transition to typical Spheroides. Spheroides maculatus is common on our Atlantic coast, the puffer, or swell-toad of the coastwise boys who tease it to cause it to swell. Spheroides spengleri and S. testudineus abound in the West Indies. Spheroides politus on the west coast of Mexico.
Fig. 357.—Puffer, inflated, Spheroides spengleri (Bloch). Wood's Hole, Mass.
Fig. 358.—Puffer, Spheroides maculatus (Schneider). Noank, Conn.
In Tetraodon the nasal tentacle is without distinct opening, its tip being merely spongy. The species of this genus are even more inflatable and are often strikingly colored, the young sometimes having the belly marked by concentric stripes of black which disappear with age. Tetraodon hispidus abounds in estuaries and shallow bays from Hawaii to India. In Hawaii, it is regarded as the most poisonous of all fishes (muki-muki) and it is said that its gall was once used to poison arrows. Tetraodon fahaka is a related species, the first known of the family. It is found in the Nile. Tetraodon lacrymatus, black with white spots, is common in Polynesia. Tetraodon aërostaticus, with black spots, is frequently taken in Japan, and Tetraodon setosus is frequent on the west coast of Mexico. This species is subject to peculiar changes of color. Normally dark brown, with paler spots, it is sometimes deep blue, sometimes lemon-yellow and sometimes of mixed shades. Specimens showing these traits were obtained about Clarion Island of the Revillagigedos. No Tetraodon occurs in the West Indies. Colomesus psittacus, a river fish of the northern part of South America, resembles Spheroides, but shows considerable difference in the skull.