Fig. 148.—Loricaria aurea Steindachner, a mailed Catfish from Rio Meta, Venezuela. Family Loricariidæ. (After Steindachner.)
Fossil Catfishes.—Fossil catfishes are very few in number. Siluridæ, allied to Chlarias, Bagarius, Heterobranchus, and other fresh-water forms of India, are found in the late Tertiary rocks of Sumatra, and catfish spines exist in the Tertiary rocks of the United States. Vertebræ in the Canadian Oligocene have been referred by Cope to species of Ameiurus (A. cancellatus and A. maconnelli). Rhineastes peltatus and six other species, perhaps allied to Pimelodus, have been described by Cope from Eocene of Wyoming and Colorado. Bucklandium diluvii is found in the Eocene London clays, and several species apparently marine, referred to the neighborhood of Tachysurus or Arius, are found in Eocene rocks of England.
There is no evidence that the group of catfishes has any great antiquity, or that its members were ever so numerous and varied as at the present time. The group is evidently derived from scaly ancestors, and its peculiarities are due to specialization of certain parts and degeneration of others.
There is not the slightest reason for regarding the catfishes as direct descendants of the sturgeon or other Ganoid type. They should rather be looked upon as a degenerate and highly modified offshoot from the primitive Characins.
Order Gymnonoti.—At the end of the series of Ostariophysans we may place the Gymnonoti (γυμνός, bare; νῶτος, back). This group contains about thirty species of fishes from the rivers of South America and Central America. All are eel-like in form, though the skeleton with the shoulder-girdle suspended from the cranium is quite unlike that of a true eel. There is no dorsal fin. The vent is at the throat and the anal is excessively long. The gill-opening is small as in the eel, and as in most elongate fishes, the ventral fins are undeveloped. The body is naked or covered with small scales.
Two families are recognized, differing widely in appearance. The Electrophoridæ constitutes by itself Cope's order of Glanencheli (γλανίς, catfish; ἔγχελυς, eel). This group he regards as intermediate between the eel-like catfishes (Chlarias) and the true eels. It is naked and eel-shaped, with a short head and projecting lower jaw like that of the true eel. The single species, Electrophorus electricus, inhabits the rivers of Brazil, reaching a length of six feet, and is the most powerful of all electric fishes. Its electric organs on the tail are derived from modified muscular tissue. They are described on p. 170, Vol. I.
The Gymnotidæ are much smaller in size, with compressed scaly bodies and the mouth at the end of a long snout. The numerous species are all fishes without electric organs. Eigenmannia humboldti of the Panama region is a characteristic species. No fossil Gymnonoti are recorded.
CHAPTER X
THE SCYPHOPHORI, HAPLOMI, AND XENOMI
Order Scyphophori.—The Scyphophori (σκύφος, cup; φορέω, to bear) constitutes a small order which lies apparently between the Gymnonoti and the Isospondyli. Boulenger unites it with the Isospondyli. The species, about seventy-five in number, inhabit the rivers of Africa, where they are important as food-fishes. In all there is a deep cavity on each side of the cranium covered by a thin bony plate, the supertemporal bone. There is no symplectic bone, and the subopercle is very small or concealed. The gill-openings are narrow and there are no pharyngeal teeth. The air-bladder connects with the ear, but not apparently in the same way as with the Ostariophysan fishes, to which, however, the Scyphophori are most nearly related. In all the Scyphophori the body is oblong, covered with cycloid scales, the head is naked, there are no barbels, and the small mouth is at the end of a long snout. All the species possess a peculiar organ on the tail, which with reference to a similar structure in Torpedo and Electrophorus is held to be a degenerate electric organ. According to Günther, "it is without electric functions, but evidently representing a transitional condition from muscular substance to an electric organ. It is an oblong capsule divided into numerous compartments by vertical transverse septa and containing a gelatinous substance."