1911 Encyclopædia Britannica/Cyprinodonts
CYPRINODONTS. In spite of their name, the small fishes called Cyprinodonts are in no way related to the Cyprinids, or carp family, but are near allies of the pike, characterized by a flat head with protractile mouth beset with cardiform, villiform, or compressed, bi- or tri-cuspid teeth, generally large scales, and the absence of a well-developed lateral line. About two hundred species are known, mostly inhabitants of the fresh and brackish waters of America; only about thirty are known from the old world (south Europe, south Asia, China and Japan, and Africa). Several forms occur in the Oligocene and Miocene beds of Europe. Many species are ovo-viviparous, and from their small size and lively behaviour they are much appreciated as aquarium fishes.
In many species the sexes are dissimilar, the female being larger and less brilliantly coloured, with smaller fins; the anal fin of the male may be modified into an intromittent organ by means of which internal fertilization takes place, the ova developing in a sort of uterus. In the remarkable genus Anableps, from Central and South America, the strongly projecting eyes are divided by a horizontal band of the conjunctiva into an upper part adapted for vision in the air, and a lower for vision in the water, and the pupil is also divided into two parts by a constriction.
The Amblyopsidae, which include the remarkable blind cave fishes of North America (Mammoth cave and others), are nearly related to the Cyprinodontidae, and like many of them ovo-viviparous. Chologaster, from the lowland streams and swamps of the south Atlantic states, has the eyes well developed and the body is coloured. Amblyopsis and Typhlichthys, which are evidently derived from Chologaster, or from forms closely related to it, but living in complete darkness, have the eyes rudimentary and more or less concealed under the skin, and the body is colourless.
See F. W. Putnam, Amer. Nat. (1872), p. 6, and P. Boston Soc. xvii. (1875), p. 222; and C. H. Eigenmann, Archiv. für Entwickelungsmechanik der Organismen, viii. (1899), p. 545. (G. A. B.)