Fig. 383.—Pectoral arch (left side) of Gastrosteus aculeatus. (After Parker.) cl, Clavicle; cor, coracoid; pt, pterygials; sc, scapula; scl, supra-clavicle.
Fig. 384.—Gastrosteus aculeatus. × 1. (After Goode.)
Four genera: Gastrosteus, Apeltes, Eucalia, Spinachia.
The little Three-spined and Two-spined Sticklebacks (Gastrosteus aculeatus and G. pungitius), which include many varieties that have been regarded as distinct species, are among the best known of our British Fishes. They are remarkable for the perfect indifference with which they can be transported from fresh into salt water, and vice versa, and for the elaborate nests which the males build in fresh or brackish water, and over which they watch with the greatest vigilance after the female has deposited her relatively large eggs.[[703]] These nests are made of weeds and twigs fastened together by threads secreted by the kidneys of the male. The larger fifteen-spined Stickleback (Spinachia vulgaris) is entirely marine; its nests are to be found on our coasts in sheltered rock-pools, and they are made chiefly of sea-weeds and Hydrozoa. Sticklebacks are short-lived, and are believed to breed only once.
The Gastrosteidae are restricted to the northern hemisphere, being more abundant in the higher latitudes, extending to Iceland, Greenland, and Bering Straits; the southernmost points of their distribution are Algeria in the Old World, and Lower California in the New.[[704]]
A very large number of species have been described, but probably only about a dozen deserve to stand.
Fig. 385.—Distribution of the Gastrosteidae.
Fam. 3. Aulorhynchidae.—The genera Aulorhynchus and Auliscus, each with one species from the Northern Pacific, much resemble Spinachia in outward form and in the equal size of the anterior vertebrae, but the snout is still more produced, tubiform, and the ventral fins are formed of one spine and four soft rays. The difference which justifies their separation as a distinct family resides in the disposition of the ribs, which are flattened and ankylosed to the lateral bony shields.