Although partly feeding on worms and other small forms of animal life, the carp is principally a vegetarian, and the great development of its pharyngeal apparatus renders it particularly adapted to a graminivorous regime.
Characters: Barbels, three to six pairs; pharyngeal teeth in one row, in moderate number; anterior part of the air-bladder divided into a right and left chamber, separated by a constriction, and enclosed in a bony capsule, the posterior part free or absent.
The mouth is usually more or less protractile and always toothless; the lower pharyngeal bones, which are large and falciform, subparallel to the branchial arches, are provided with teeth, often large and highly specialized, in one, two or three series (pharyngeal teeth), usually working against a horny plate attached to a vertical process of the basioccipital bone produced under the anterior vertebrae, mastication being performed in the gullet.
Correlated with the presence of the genital pleurae there is a pair of vascular folds of the basement membrane proceeding from the dorsal wall of the gut in the postbranchial portion of the branchio-genital region, and from the dorsal angles made by the pleural folds with the body-wall in the pharyngeal region; they pass, in their most fully developed condition, to the free border of the genital pleurae.
The Cyprinidae' are divided into four subfamilies: - Catostosninae (mostly from North America, with a few species from China and eastern Siberia), in which the maxillary bones take a share in the border of the mouth, and the pharyngeal teeth are very numerous and form a single, comb-like series; Cyprininae, the great bulk of the family, more or less conforming to the type of the carp; Cobitinae, or loaches (Europe, Asia, Abyssinia), which are dealt with in a separate article (see LoAcH); and the Homalopterinae (China and south-eastern Asia), mountain forms allied to the loaches, with a quite rudimentary air-bladder.
In them the foot has a flat ventral surface used for creeping, as in Gastropods, the byssus gland is but slightly developed, the pleural ganglia are distinct, there is a relic of the pharyngeal cavity, in some forms with a pair of glandular sacs, the gonads retain their primitive connexion with the renal cavities, and the otocysts are open.
The perforated pharyngeal region has then been detached from the adherent epipleura or opercular folds (wall of atrial or branchial chamber) by cutting the fluted pharyngo-pleural membrane d, and separated by a vertical cut from the intestinal region.
Ph.N.,as itself, which communicates with the pharyngeal notch.