Fam. 4. Mugilidae.—Maxillary excluded from the border of the upper jaw; dentition feeble or absent. Body covered with cycloid scales. Ribs attached to the extremity of strong parapophyses. Pectoral fins inserted high up; ventral fins more or less approximated to the pectorals, with one spine and five soft rays; pelvic bones suspended from the post-clavicles. Two well-separated dorsal fins, the anterior formed of a small number of spines. Air-bladder present.
These Fishes are closely related to the preceding, of which they are a further specialisation, the pharyngeal bones having a complicated structure, much reducing the oesophageal opening, and the vertebrae being reduced in number (24 to 26 instead of 32 to 60). They feed on organic matter contained in mud, and inhabit the fresh waters and coasts of the temperate and tropical regions. The species number about 100. Principal genera: Mugil, Myxus, Anostomus, Joturus. Grey Mullets (Mugil) are represented on our coasts by three species, valued as food, one of which (M. capito) has a remarkably wide range, occurring from Scandinavia to the Cape of Good Hope. Remains referred to the same genus occur in the Miocene and Oligocene.
Fig. 391.—Shoulder-girdle and pelvis of Polynemus quadrifilis. cl, Clavicle; cor, coracoid; pec, pectoral rays; pel, pelvis; pt, pterygials; ptcl, post-clavicle; pte, post-temporal; sc, scapula; scl, supra-clavicle; ven, ventral rays.
Fam. 5. Polynemidae.—Maxillary excluded from the border of the upper jaw; dentition feeble. Body covered with ctenoid scales. Ribs attached to the extremity of strong parapophyses. Pectoral fin inserted low down, with a lower portion consisting of free rays; the upper portion, or fin proper, attached to the scapula, the lower to a fenestrate bone which appears to be formed by coalesced pterygials (Fig. 391, pt.). Ventral fin more or less approximated to the pectoral, with one spine and five soft rays; pelvic bones suspended from the post-clavicles. Two well-separated dorsal fins, the anterior formed of a small number of spines. Air-bladder, if present, very large.
The vertebrae number 24 (10 + 14).
Fig. 392.—Polynemus quadrifilis, × ¼. (After Cuvier and Valenciennes.)
Three closely allied genera: Polynemus, Pentanemus, and Galeoides, with about 25 species, from the shores of tropical seas, often entering rivers. Some attain a length of 4 feet, and are valued as food or for the isinglass yielded by their air-bladder. The free pectoral filaments are organs of touch, and can be moved independently of the fins.
Fam. 6. Chiasmodontidae.—The deep-sea genera, Chiasmodon, Pseudoscopelus, and Champsodon, which have been placed either with the Gadidae, the Trachinidae, or the Berycidae, may be referred to the Percesoces, as the pelvic fins have only a ligamentous connexion with the pectoral arch. Unfortunately, the skeleton has only been examined in Champsodon; it is remarkably similar to that of the Atherinidae. As in Atherinichthys, the posterior extremity of the air-bladder is protected by a bony sheath formed by the expanded ring-like haemal processes of the anterior caudal vertebrae. Vertebrae 32 (16 + 16). The scales are absent or very small and spinulose, the mouth large, with cardiform teeth; spinous dorsal short, soft dorsal and anal elongate. Chiasmodon and Pseudoscopelus have a complicated system of sensory organs on the body, which in the latter suggest the photophores of Scopelids. Champsodon vorax is a fish of extreme voracity, swallowing prey much larger than itself. Only four species of this family are known.